606 



GARDENERS' CHRONICLE 



Plant Distribution 



WILLARD N. CLUTE 



A DISPOSITION to move from one locality to an- 

 other seems characteristic of all living things. 

 Alan himself is a good illustration of this fact, 

 for his spirit of unrest among familiar scenes has 

 prompted the more venturesome to explore distant lands, 

 inspired the fisherman, hunter, and student to ramble 

 nearer home and sends all of us away on at least two 

 weeks" vacation. Possibly it is this spirit, also, that in- 

 clines a great number to change residences annually. 



The migrations of birds are the most conspicuous ex- 

 amples of change of locality in the animal world, though 

 of course it is well-known tliat many fishes regularly 

 migrate and that the habit extends to various mammals. 

 The annual movements of the great herds of buli'alo 

 which once peopled the western plains are now but 

 memories, but the fur seals still have their migrations. 

 and many other illustrations will be recalled, including 

 such annual excursions as the garden toad makes to the 

 nearest pond for the Spring mating. These expeditions, 

 however, differ from the changes first referred to inthat 

 migrating forms ultimately return to the place from 

 which they came. There is to be distinguished from this 

 a movement away from the common center which results 

 in colonization and permanent occupation of regions far 

 from home. 



There are few plants that make regular migrations, 

 though the habit is not entirely absent among the simpler 

 forms, but in the wider field of exploration and coloniza- 

 tion, ]3lants are second only to man himself. One of the 

 chief incentives for man to move into a new region is 

 the chance that he may better himself by so doing, and 

 this seems to be the main advantage in plant movements. 

 The two differ in this, however : man moves as an in- 

 dividual ; the plant as a species. The latter cannot go 

 itself, but it sends its children. No living thing is com- 

 pletely adapted to its locality : it does the best it can un- 

 der the circumstances. When the chance to occupy a 

 new locality presents itself it may often do much better 

 by moving into it. Our wild plants aff'ord many illustra- 

 tions of this truth. They may be obscure and harmless in 

 the region in which they are native, but transported to 

 new countries they may become pestiferous weeds. The 

 career of the prickly pear in Australia, of the Russian 

 thistle in our semi-arid West, of the orange hawkweed, 

 the oxeye daisy, the buttercup, and the Canadian thistle 

 are good examples. All indicate that the region in which 

 a species originates is not necessarily the one to which 

 it is best adapted. 



Unless the situation in which a plant finds itself is de- 

 cidedly favorable it can never become a weed there. It 

 may, and often does, find a region distinctly unfavorable 

 and may fail to get a root-hold at all. The problem is 

 further complicated by the fact that in ordinary situations 

 all the available ground is already occupied while multi- 

 tudes of seedlings, native to the region, annually spring 

 up to compete for the places left vacant by the death of 

 other individuals and to endeavor to overcome the least 

 aggressive of those still living. Well established plants 

 often find themselves hard pressed by such circimistances 

 and it is no doubt fortunate for them, or at least for their 

 race, that the)' are equipped with various devices for mov- 

 ing elsewhere. 



There are certain associations of plants here and there 

 so adjusted to soil and weather and to one another as to 

 render the chance for a new plant's getting in extremely 

 small. Such associations have usually lasted a long time 



and have reached their present state only after a vigorous 

 struggle in which all weaklings were ousted. In other 

 places, however, this nicely balanced arrangement may 

 be unsettled by various natural causes and thus offer an 

 invading species more hopes of success. A landslide, for 

 instance, may carry down into a valley all the plants over 

 a considerable area and thus throw that region open to 

 settlement. Moreover, the soil and rock carried down 

 may dam a stream and form a lake or pond which drowns 

 out the original inhabitants but forms a congenial home 

 for water plants. Lakes are constantly being filled by 

 earth and leaves washed into them or drained by streams 

 cutting down their outlets. Rivers in flood gnaw away 

 the banks in one place only to deposit the material in 

 another in the form of sand-bars, islands, deltas or flood 

 plains. Alan, himself, has extensively changed the face 

 of Nature by filling, draining, burning, logging, quarr}-- 

 ing, mining and the like. All these afford new regions for 

 colonization. JMost serious of all from the wild plant's 

 situation, are the operations of the farmer which remove 

 whole floras to set new plants in their stead. Incidentally 

 very extensive opportimities for colonization are pre- 

 sented, but they can be taken advantage of by only the 

 most aggressive of plants, that is, the weeds. 



When plants spread into a region that for some reason 

 is thrown^ open to a new population, the first species to 

 spring up, as might be expected, are those with wind- 

 borne seeds. Plants with jiticy fruits commonly follow 

 and those with burs and nuts come last. There is also 

 a regular order in the plants themselves, the first comers 

 being largely annuals and biennials. Herbaceous peren- 

 nials are somewhat slower to invade a region and the 

 shrubs and trees are slowest of all. It may be said, how- 

 ever, that the first plants in a region are not necessarily 

 those capable of holding it. It requires a certain amount 

 of persistence to win, as in other walks of life, and the 

 slower growing perennials ultimately prevail. There are 

 many cases, also, in which plants may spoil a locality for 

 themselves and yet make it favorable for others. In a 

 cat-tail swamp, the accunnilation of dead vegetation may 

 finally produce a soil that other plants can take and hold. 

 In nearly every locality one may find indications of one 

 group of plants giving way to others. 



There are few plants lacking in some special means for 

 moving from one locality to another, but any of these 

 means may fail to function in certain situations. Thus it 

 is that many plants able to thrive in a given region are 

 yet unable to reach it b}' reason of barriers of one kind 

 or another. To woodland plants, a wide area of grass- 

 land or desert would be an insuperable barrier, just as 

 the forest would be a barrier to grassland species. High 

 mountains may prevent plants which cannot endure the 

 cold from passing and at the same time may oft'er a route 

 along which northern plants may spread far southward. 

 Thus we see that what is a barrier to one species is not 

 necessarily a barrier to another. The sea is an unusually 

 eft'ective barrier to the spreading, not only of plants, but 

 of animals, and has often been depended upon to protect 

 one country from the injurious species of another. This 

 has not, however, prevented many European weeds from 

 invading territory, nor will it entirely protect us from 

 others. 



What men want is not talent, it is purpose : in other 

 words, not the power to achieve, but the will to labor. 

 I believe that lalxir judiciously and continuously applied 

 becomes genius. — Selected. 



