March 19, l8 98. 



GARDENERS' 



MAGAZINE. 



T 



G 



D 



of Plants 



There is no fact better established in geology than that the earth's crust is not 

 stable, but is constantly undergoing extensive changes and subsidences ; this brings 

 it to pass that land and water surfaces are not constant but changing, and that 

 many regions now separated by the sea have in former times been connected, and 

 many now connected have but lately become so. These changes have forced 

 vegetation to perform migrations which have been small or extensive, slow or 

 rapid, just in proportion to the change, and these have been accompanied by great 

 changes in climate, including even such extreme conditions as prevailed in the 

 glacial period. 



5 Alpine Floras. 



In looking at the distribution of plants in a broad way, the first feature to 

 strike attention — according to Mr. W. F. Ganong, of Harvard University, in a 

 lecture delivered to the Massachusetts Horticultural Society — is the constancy with 

 which upon higher mountains we find plants characteristic of regions far to the 

 north of them in the northern hemisphere and far to the south of them in the 

 southern, and in all cases cut off from their brethren by many valleys and plains 

 occupied by wholly distinct species. Thus upon the Rocky Mountains, the Alps, 

 the Himalayas, and others are herbaceous plants which are found growing at the 

 sea level around the Arctic Ocean. Farther down these mountains come plants 

 which grow in southern parts of Alaska, Labrador, Northern Scandinavia, and 

 Siberia. Now, it is plain why they can live there— the heat and moisture condi- 

 tions upon the mountain side and at the sea level farther north are similar, as we 

 have seen ; but how did the plants get upon the mountains from the north ? The 

 natural means of spread of the species themselves are hardly sufficient to 

 explain it. But the solution is undoubtedly found in late geological history. 

 In the glacial period, geologically very late, there descended from the north a 

 great ice sheet of enormous thickness which drove all vegetation before it. It 

 came so far down that Arctic plants were driven south of the region in which we 

 are now living, and Arctic plants flourished all across the United States just south 

 of a line from about forty degrees north latitude on the Atlantic coast, running 

 diagonally northwestward and in corresponding regions in the eastern hemisphere; 

 Along the high mountain ranges these plants extended much farther south, finding 

 upon them their natural conditions of heat and moisture. Then the ice sheet 

 retreated ; the Arctic plants followed it, each tending to return to its own latitude 

 Bat along the high mountains the conditions did not change much, and the 

 Arctic plants found upon them homes, where the species of the lowlands 

 could not compete with them. In the valleys, however, the more southern species 

 were at home, and soon drove out the Arctic intruders. So widespread and 

 definite was this agency that there has not been a mountain range explored in the 

 northern hemisphere upon which traces of these Arctic plants have not been 

 found ; moreover, the lower ranges, those not high enough to reach the line of 

 perpe ual snow, like the White Mountains, have not the extreme Arctic forms upon 



X S'hm ™S^ C 5 C ,° ld tempCrate f ° rmS > and these extend so P u± 



wiZJt ^ ^ ^ 8 a f *7 g °-. f Very interestin £ P oi *t in connection 

 Hith this is the fact that in the glacial period some of the Arctic and sub- Arctic 



Ind w ge M° Cr ,° SS th " e ^ Uat0r alon g the hi S hest mountain chains o^nf Old 

 thl f Y° r,d l and eSUb lshed thems elves in the southern hemisphere and a e 

 there found on the mountains at the present day. Hence we have T™t MtuS 

 group of plants called the Arctic alpine flora, consisting 



rimiw' ,r C °1 d fea i U ', e is that in the scathe™ hemisphere, we have a verv 



£S£St TefJads ,£ n,arCtk 1,pin ? - foaVd 2 



•he mountains of ChiB Aii^rSn, s ° uth « n .<» : « n . »«d extending northward upon 



S&s & ess g is p P 5d. that " fa be,ieved ta 



p Temperate Floras. 



the northern \n?\£ loXTn'h^t' ^ * T'l marked Contrast b *ween 

 -the oiduaa^^^^^^^. In ^ former we find the plants 



Asia, and America to be • "v"* WC across Europe, 



the plants of dSSn regions ^, ^H in f C J aract f* f n ? th * differences between 

 forms than of differenced ^in thl f n rathe f r , those , of relatlv * richness or poverty in 

 "gain. Hence, wi n th exc<£f Jn T then ) s ? ^7* P oint to which I will refer 

 and western mSiS^SSS? lu^fl °t assembla S e the Caucasian 

 ^ grouped into one Tora S £1 * t P ? ? n ° rthem tem P«ate zone 

 nch exception of whTch I snok i ^rediate or temperate flora, and the 



Jora. This latter is Sifflv riS^? ia ^ ,y ^ ^editerraneo-Caucasian 

 belonging to it Sw t £ 8 V • s P ec }9> Slx " seve nths of those of all Europe 



^lly expfaineJ I by iZi^^^J*?** n ? tthe ™ temperate flora is ve?y 

 several points in Greenland sTLhY c ■ AfC T d , the ° cea n, and at 



abundant fossil deposks of nlam S, ! ^"t' P laces > there « found 



the remain, of t he^ncestor s of our 1 i v^Ta^f ^ WhlCh foSsils are undoubtedly 

 1 i h ! s P? c -s of the S S and < 5tiZ£S*±^5£ W ation - Not only 



This 



n the chaSS aftSSS 1™ X? * ^t'- **** " we ha - notfoed/and 

 In E SeVCrely - OCCSS an retUm northward Parts of it 



than our own* ^ThSCi'f 5"- th ! "Y 551 P art a P oor one > having much fewer SDecies 

 J" 'ranges run l^tTlt^^ ^ ?n EuropeThTmoun! 



fcK° f ^ entral Europe were ~LhA t g ^ a ^anced southward, the 

 'rom the Pyrenees Air? Y caught between it and the increasing local pfeHm 

 «<*pe, ma y n ; ne o e f s ' £l£ Apennmes, and Caucasus ; there being^ttKhanSTS 

 na tural mean J 0 f w d e — exterminated > Particularly Those not Ravine 



Tk>°* the ShZt^TT^T' ^ m u any v r ° f th0Se wh > ch escaped the Toy 



to re-cross when the SjS*? • the Medi terranean. Thi S P they were 



™ jould return^ theh ^horn^ ^ e " She -" tre " ted ' and but few of ^eriS 



nonJ lid J? n m ? Ca aDd j n Eastern Asia ' IIere the m °untain ranges run 

 Sie sea ? 7 SO ' and ^ Asi * the great ranges end before thef reach 



5h£»'. way IS retu3 ^ OP , en ^ Which the P lants travelled ^th out 

 of Ea^rn A^Jtt turned again when the enemy retreated. Hence, the floras 



moSl SEn E Jf ern ^ are both exceedingly rich in specks and 



"SiS^glS trme^^ PrCSerVed nea ^ a » JL ^ Sroujh ^ 



Peculiarities of Distribution. 



AmSica f%M> T ! hC - fl ° ra ° f WeStern America rich lik * that of Eastern 

 America ? Thi s question is not so easy to answer. It is true the Rockfos V™ 



I"** S - k f J . Wh J WCre DOt a11 the ^ estern P^nts preserved ? Setrafcauses 



rSnn t r^ t0 deStWy ^ one of which ' s th e extreme unevennes of the 

 region west of the great mountains, and hence the crowding and exLrminatfon of 

 some species, and also the fact that the very uniform climfte of S HforoS ^ is not 

 so favourable to the northern species accustomed to more variabl T coS on ^s i 

 is to the more southern forms of Mexico ; and these latter have travelled S larVe 

 numbers into Cahfornia, and possibly by direct competition haTexTerminifd 

 IZt T?<\l nd Certain , other g eol °fcal conditions have doubtless ^ conSted 



remains that, like that of Fnrnnp th<> 



A°Zrt C ? T hf ° rnian r ^° n is P° or in tem P erate s P e ^^. while those of Eastern 

 America and Japan are rich and much alike. eastern 



t u „ n B the s °u ther " hemisphere we find a very different state of things. There 



flZ?It? -Z 0n TT 5 J ^ t&ted from ^ch other from a most remote period, possess 

 floras strikingly distinct from each other, so that it is necessary to assien to each 

 great body of land its own distinct flora. This gives us the Aus tin flora 

 showing some slight traces of connection with the region to the north oHt, and 

 wi h New Zealand. Australia has so long been separated from the other bodies 

 of land that its flora has had time for a great deviation from that of other countries 

 Indeed, it is notorious for its unlikeness to that of any other country. Next, the 

 Andean flora that of South America, which shows some slight connection with 

 that of New Zealand and Australia. 



Then the Mexico-Californian flora which extends up the west coast of 

 America from Chile to Mexico and into California, being the source of many of 

 our present Cahfornian species ; and lastly, the South African flora, one that is 

 very rich m species aud remarkably varied. And just as our north temperate 

 plants have representatives on the mountains far south of them, so these southern 

 noras have some of their members on mountains far away to the north "The 

 plants of Fuegia extend northward along the Andes, ascending as they advance " 

 Australian genera reappear in Borneo, and even cross to China and Japan : New 

 Zealand forms are upon the mountains of New Caledonia ; South African in the 

 lake region of Africa, in North Africa, and even in the Canary Islands and Asia 

 Minor, in all these cases the southern, like the northern, forms ascend the moun- 

 tains as they approach the equator, and descend toward the sea level after they 

 have crossed it. Now, what is the history of these widely-separted regions ? There 

 seems every probability that in times far back all these floras came, not from the 

 south, but from the north ; and the time when they had a common home there is 

 so remote that the floras have had time to diverge greatly. That this is the correct 

 view is sustained by the fact that these southern floras are much more like those 

 immediately to the north of them than they are like one another ; that there is no 

 evidence of a southern continent from which they could have come ; that while 

 most peculiar species of the south have relatives, either living or fossil, in the 

 north, none of the northern forms have fossil relatives in the south. 



Floras of the Tropics. 



Lastly we come to the tropical floras, characterised by great abundance of all 

 kinds of vegetation, and with a preponderance of succulent, moisture-loving 

 plants. Of these there are three, remarkably distinct, if we consider the 

 relationship of the plants of which they are composed ; very similar if we consider 

 their general appearance. They are : the American flora, reaching its highest 

 development in the valley of the Amazon. It is excessively rich in species and 

 luxuriant in growth. Secondly comes the African flora, still imperfectly known, 

 but also very rich. Many of its general characteristics have been vividly sketched 

 for us^ in Mr. Stanley's latest work. And thirdly is the Indo- Malayan flora, 

 including India and all the East Indian Archipelago, with the Malay Peninsula, 

 and extending even to Australia and Japan. The relationships of these three are 

 sufficiently well known to indicate that while they differ much from each other, 

 they are more alike than are the floras of the south temperate zone we have con- 

 sidered, a fact tending to show that the former may have been connected with each 

 other more recently than the latter. From this the step is but a short one to the 

 theory some years ago propounded by an English naturalist, that all the floras, and 

 therefore all the plants of the earth, have originated in the northern hemispheres 

 and that they have spread southward in successive great waves, the more southern 

 and older floras being the most an ient of these, the more northern floras later in 

 time. 



In conclusion, to sum up the whole matter, I hope I have shown that while the 

 causes controlling the distribution of plants are many, and rendered tremendously 

 complexed by their interaction, we can separate out the principal agencies and 

 trace their effects ; that the agencies Umiting distribution are, the needs of plants 

 with reference to the amounts of heat and moisture to which they have respectively 

 become adapted, and also by the past history of each plant, placing it in some one 

 region, and not in all to which it is adapted ; and finally, that the active 

 distributing agent, aside from the comparatively feeble efforts of the plants them- 

 selves and man's insignificant effect, has been the successive migrations compelled 

 by past climatic and geological changes, and these migrations have resulted in the 

 distribution of all plants over the earth's surface into those different groups or floral 

 which we have just considered, which groups probably all came in a series of great 

 waves from the north. 



Forced Rhubarb.— How welcome at any time, but especially in such a 

 season as the present, when apples are scarce and dear, is forced rhubarb. Yet, 

 all the same, how exceedingly dear it is ! Sold in bundles of three stems tor 

 threepence, or at the rate of one penny per stem of about twenty inches in length, 

 no wonder it is not for the million in the middle of March, as it will be some few 

 weeks hence. But it seems as if there is great room for an expansion of rhubarb 

 forcing. What may be the price obtainable by the grower it would be 

 interesting " " T ' " 



I rende n t0 their homes a^ain Th th' u exiled w ~™ , ™ — r Mtw .~ 



Uede^% ? ear, y ce *tain bv the fj thJthLi r true cour se of events gooseberries are about the same price relative to product, as these do not shrink, 



kcial Sh ln Central Europe, showin^at the^ eTiT d h " ^ fOUr?d f ° SSil in and they are qdteaS palatab,e ** are those S athered in Tune. Whilst it does seem 



ire^nioii 1 ; \ Central Asia hac ~~J? . ...rr_ 1S , . tnere . anterior to the 



and they are quite as palatable as are those gathered in June. v*« w 

 as if the pulping or jam-making of fruit was rather overdone, there seems no 

 doubt whatever but that good bottled or tinned whole fruits are in great request, 

 and there is not the least probability that the public taste will varv. errenf in thp 



very direction of wanting much more 



