150 



KNO\VLi:i)Gi:. 



Al'kli.. 1912. 



It will 1h' rememlicrt'il that (as Mr. ICdcliiiKton rccciilly 

 pointed out) tlif M stars are ititriiisicaily faint, liaviiij; 

 strongly absorbiiiK atmospheres; conse<|nently. they cannot 

 be seen at a distance, which is the reason why the Sun's 

 nearer neigbbours contain an apparently nndne proportion of 

 M stars : they are probably really as common in the more 

 distant p.irts of space, bnt too faint for us to see. Conversely 

 the li stars are all very distant, and are probably .ictually rare 

 in space, bnt beintj of great intrinsic brilliance they are seen 

 at ininicnsc distances, and so appear in exaggerated numbers 

 in our catalogues. The Sirian type of spectrum of (Galactic 

 stars would also be e.Yplained by stars of the solar type being 

 invisible at such a great distance. 



A NfiW STAR. — A new star of the fourth magnitude was 

 discovered at Kiel on March IJth. It is stated to be near 

 Thet.i ("ieminornni (the same region where Professor Turner's 

 Nov.i .ippeared in March, 1903). 



BOTANY. 



By Professor F. Cavf.ks, D.Sc, F.L.S. 



POTASSIL'M IN PLANTS.— Some interesting results 

 bearing upon the localisation and function of the element 

 potassium in plants have recently been published by Weevers 

 (Rec. Trav. Nccrlaiul. , \'lll.. I'Jll), who made numerous 

 tests by means of Macallum's method for the detection of 

 potassium — the jjrecipitation of potassium-cobalt-nitrite and 

 the conversion of this into the black sulphide of cobalt by 

 treatment w^ith anmioniuni suljjhide. 



Weevers found potassium in the tissues of all the plants he 

 examined, covering a wide range, excepting in the blue-green 

 algae (Cyanophyceae) which gave negative results. In no 

 case, however, was potassium to be found in the nucleus, even 

 when abundant in the protoplasm of the cells. Even more 

 surprising, in view of the statements of previous writers, was 

 the entire absence of this element from chlorophyll and from 

 the chromatophores themselves. The greater portion of the 

 potassium was found in the cell-sap vacuoles. In every case 

 the potassium was present in a form soluble in water, and it 

 could be extracted by means of water or dilute alcohol, but 

 was insoluble in ether. In the flowering-plants, this element 

 is most abundant in the ground-tissue (parenchyma), especially 

 in the growing-points and in reserve-food organs. It is also 

 present in the living parenchyma of the wood and barU of 

 trees, and particularly so in the growing-layer (cambium) and 

 in the medullary rays, which appear to serve as storeplaccs of 

 potassium for the growth of new shoots. 



As to the functions of potassium, Weevers concludes from 

 his observations that this element plays little or no part in the 

 process of carbon assimilation, but is probably concerned in 

 the building-up of protoplasm at the growing-points and in 

 growing tissues generally. In the leaves, it probably helps in 

 the synthesis and also in the breaking-down of proteins. 



BIOLOGY OF LICHENS.— An interesting paper by 

 Tobler on the mode of nutrition of lichens was noted some 

 time ago in these colunms (" Knovvi.kdgk," 1911, page 276). 

 The same writer ijithrb. fiir iciss. Bot., 1911) has since 

 published a longer paper — the first instalment of what 

 promises to be an important series of researches — in which he 

 deals with the relation of two so-called " lichen parasites," 

 both belonging to the Peziza family of fungi, to (1) the lichen 

 host itself, to (2) the alga component of the lichen, and to 

 (3) the substratum on which the lichen grows. 



The fungus Phacopsis viilpiita grows on the lichen 

 Eventia viilpina. an alpine species. Tobler sectioned 

 the fungus and lichen together in paraffin, and traced the 

 course of the Phacopsis hyphae in the lichen thallus. These 

 threads reach the enclosed alga cells and grow closely around 

 these. Where the Phacopsis is best developed on the lichen, 

 the alga cells are entirely absent ; on other regions the algae 

 are surrounded singly or in groups by the Phacopsis threads ; 

 in other places the hyphae of both Phacopsis and the lichen- 



fungns are foimd entwining llic .ilgae. Hence the Phacopsis 

 threads can in lime reach the algae in certain areas of the 

 lichen thallus and displace the threads of the lichen-fungus 

 itself. The algae apparently multiply more rapidly for some 

 time after the Phacopsis threads reach them, but they finally 

 disappear entirely where these threads are most profusely 

 developed. The Phacopsis threads then spread laterally 

 until large portions of the Evcniia cortex are cut off from the 

 central tissue (mednll.il and eventually die. the invading 

 threads then penetrating inlr) the dead cortex and also into 

 the medulla of the lichen. Tobler concludes that the 

 Phacopsis is at first a " parasytnbiont," living in partnership 

 with the lichen and later becomes parasitic. 



The second parasite investigated. Karscliia dcstructans. 

 grows on the th.illus of Cliaciiothcca clirysoccphala. a bark- 

 inhabiting lichen with thin crustaceons thallus. 'ihc Karscliia 

 penetrates into and through the lichen th.illus and into the 

 bark itself, on its way entwining and destroying alga cells and 

 displacing and destroying the hyphae of the lichen. Finally, 

 however, the Karschia threads enter the bark and then pro- 

 duces its spore-fruits. Hence Karscliia is successively a 

 parasymbiont, a parasite, and finally a saprophyte. 



From his study of these two fungi, out of about four 

 hundred known to grow on lichens, Tobler concludes that 

 there is no sharp distinction between parasites, parasym- 

 bionts, and saprophytes among these lichen-infesting fungi, 

 since a single species may exist in all three conditions during 

 its life history. He also claims that his researches break 

 down the supposed sharp boundary between lichens and 

 fungi, and his interesting observations certainly appear to 

 support the view that the biological distinction between 

 lichen-fungi and other fungi cannot serve any longer to main- 

 tain the lichens as a separate group of plants. That is to 

 say, followed to their logical conclusion, Tobler's results lead 

 us to the view that the fungus alone constitutes the lichen, 



THE BUCKWHEAT SEED.— In many text-books the 

 seed of Buckwheat, so commonly used as a type for 

 germination in elementary botanical teaching, is said to 

 contain perisperm, i.e., nutritive tissue derived from the 

 nucellus tissue lying outside of the embryo-sac and within the 

 integument of the ovule, and this character has been regarded 

 as an indication of affinity between the buckwheat family 

 (Polygonaceae) and the Pepper family (Piperaceae). Stevens 

 {Bot. Gaz.. 1912) has made a carefulstudy of the development 

 and structure of the Buckwheat seed, and finds that it 

 contains no perisperm at all. The early development of the 

 embryo agrees closely with that of the familiar and often- 

 figured Shepherd's Purse iCapsclla), and accompanying the 

 growth of t'oe embryo there is rapid development of endosperm 

 from the contents of the embryo-sac. The nucellus is at an 

 early stage present as a thin, but actively-growing layer, just 

 within the integument, but as the seed matures this incipient 

 perisperm is obliterated and in the ripe seed it is represented 

 only by crushed remains of cells. 



.'\NTS .^NI) PL.'XNTS. — .An interesting paper on this sub- 

 ject has recently been published by Ridley (.4/i;i. Bot.K who, 

 as director of the botanical gardens at Singapore, has had 

 exceptional facilities for the study of the myrmecophilous 

 plants of the eastern Tropics. The cases of symbiosis between 

 ants and plants dealt with in this paper fall into three 

 categories. 



Many such plants [c.}>.. Dischidia raHicsiaiia and several 

 Rattans) afford shelter to ants, either within the leaves and 

 flowers or in special hoUowed-out organs such as tubular stems 

 or thorns, but the ants get no food from the plant, nor do they 

 appear to benefit the latter, except that in a few cases the ants 

 may bring about pollination when they nestle in and about the 

 flowers, c.^.. in Goitiothalaiiius ridlcyi. 



In a second class of myrmecophilous plants there appears 

 to be a relationship, which is mutually advantageous, between 

 many epiphytic ferns and orchids, whose roots afford shelter, 

 and the ants, which in making their nests bring up large 

 quantities of soil and heap it round the base of the plants, e.g.. 



