340 



KNO\VLi:nGE. 



SUPTKMHER, 1912. 



revisinK I lie star magnituclcs of the Cape rhotoRrapliic 

 DurchiniistoniiiK. and that it will soon be possible to refer 

 these to the standard Harvard system, which will greatly 

 increase their value. 



BOTANY. 



By Proikssor F. Cavers, D.Sc, F.L.S. 



ORIGIN OF V.^SCULAR PLANTS.— Although Pro- 

 fessor Campbell diies not in his memoir (on the Eusporangiatae 

 mentioned in last month's " Knovvlkijge,") discuss the wide 

 question of the origin of the vascular plants as a whole, he 

 re-states the arguments which he has already brought forward 

 in support of his view that Ophioglossiii)! represents the 

 most primitive living vascular plant, and that it is connected 

 with the Bryophytes (liverworts and mosses) through the 

 remarkable Antlioceros group, which is usually classified 

 with the liver-worts, thoui'h differing from all other Bryophyta 

 in some respects. 



Setting aside the question as to whether the Ophioglossales 

 or some other Ptiridophyte group (such as the Lycopods) are 

 to be regarded as the most primitive of vascular plants, there 

 are several possible views regarding the origin of the higher 

 plants. Of these, the one which has been so ably urged by 

 Campbell himself is that from some form like Antlioceros, in 

 which the spore-producing generation remains with its lower 

 portion embedded in the se.xual plant, the free-living spore- 

 pi'oducing plant of a simple Pteridophyte, not unlike Ophio- 

 alossu 1)1, m&y have arisen. The first, and perhaps the most 

 important, step required is the production of a root. The 

 sporogonium of Anthoceros obtains water and salts from the 

 simple thalloid sexual plant by means of a swollen absorbing 

 organ or foot ; above this there is a zone of active tissue, which 

 for a long time adds fresh tissue to the long cylindrical capsule 

 above ; through the capsule there runs a central bundle of elon- 

 gated cells, and the spores are produced in a zone between this 

 and the several -layered capsule-wall, which contains abundant 

 chlorophyll and bears stomata. -Apart from its supply of 

 water and salts, which are derived from the sexual plant, the 

 4«</ioceros sporogonium is self-supporting; if it produced a 

 root and sent this into the soil, it would become wholly self- 

 supporting, and we should, in fact, have something compar- 

 able to a simple form of Opliioglossuin in general organisation. 

 In the case of the existing species of Ophioglossitm. the 

 simplest type (O. moluccanum) has no definite stem, and 

 consists simply of leaf and root. The young sporophytes of 

 Antlioceros and Opliioglosstini show considerable resem- 

 blance, both having a massive foot, while the spore-capsule of 

 the former is represented in the latter by the first leaf or 

 cotyledon. Campbell regards this cotyledon, now sterile, as 

 having been, in an ancestral " pTo-Opliioglossitni " a fertile 

 structure. 



While one might point out a considerable number of detailed 

 differences between the Anthocerotales and even the simplest 

 of the known Ophioglossaceae, one must admit that this strik- 

 ing hypothesis of a direct connexion between the Bryophytes 

 and Opiiioglossnm involves, on the whole, less formidable 

 assumptions than those which confront the other theories put 

 forward to account for the origin of vascul.ar plants. 



INTENSIVE ECOLOGY.— In " Boden uiid Klima anf 

 kleinstem Raum," pubUshed by Fischer of Jena, G. Kraus 

 has produced an admirable work which will doubtless lead to 

 similar researches on various types of plant-habitat. The 

 perusal of much of the literature of Plant Ecology hitherto 

 produced, leaves one very sceptical as to the soundness of the 

 foundations upon which many of the conclusions put forward 

 are based, and for this reason one welcomes the increasing 

 number of memoirs dealing in detail with some selected habitat 

 and analysing as minutely as possible the various factors of 

 the environment — in short, attempts at what may be termed 

 " intensive Ecology." 



Kraus first deals with the influence of the lime-content of 

 the soil in his district (Karlstadt-on-Main), upon the flora, and 

 gives the results of analyses, showing the composition of the 



underlying rocks (s.mdstone, chalk, loess), subsoil, and soil ; 

 the carbonate-content at different depths in the sub.stratum 

 and in areas inhabited by different plants ; the lime-content of 

 the various plants themselves, and so on. From these analyses 

 he finds that none of the plants ex.imincd occur exclusively on 

 a substratum ol approximately c(|ual lime-content ; but on the 

 other hand some species " prefer " a high percentage of lime 

 and others a low percentage. .Among the characteristic 

 species of the sandstone areas, usually free from chalk, there 

 occur chalk-loving plants in places where some Hme is present ; 

 in these places the lime-content is usually much lower than in 

 the normal habitats of these plants, and characteristic chalk- 

 plants with high lime-percentage do not grow in such places. 

 Where the s<'uidstone merged into the limestone the author 

 found some cases of typical chalk-plants, like Hippocrepis 

 (Horse-shoe Vetch) and Pulsatilla (Pas(|ue-flower). growing 

 in places where calcium carbonate was entirely absent ; while 

 " calcifugous " (chalk-avoiding) plants, like Vacciniuni (Bil- 

 berry) and Calluna (Ling), were found in spots where a fair 

 percentage of chalk was present. In fact, excepting for a few 

 plants which apparently need large amounts of carbonate of 

 lime, Kraus found most of the " calcicolous " species on soil 

 (|uite free from carbonate, and he concludes that it is not the 

 calcium carbonate, but the physical characters of the soil, that 

 can explain the distribution of the plants. 



Of course, the facts that various "chalk-plants" may be 

 found on soils free from calcium carbonate, and that on the 

 other hand species which usually avoid lime may occur here 

 and there on chalk or limestone, have frecjuently been observed ; 

 where calcium carbonate rocks (chalk and limestone) occur 

 alongside of non-calcareous rocks, this wandering of the 

 plants from calcareous to non-calcareous soils appears to be 

 fairly common. Kraus sets out to explain this, and suggests 

 that the most important factors are the dryness and warmth 

 of the chalk-soil. He proceeds to investigate in detail, with 

 elaborate tables, the physical characters of the substratum — 

 soil structure, water content, temperature, relation of soil 

 temperature to air temperature, air temperature at different 

 heights above the surface, atmospheric humidity, and wind. 

 From his careful observations on these points. Kraus concludes 

 that the chalk substratum is by no means uniform, but is a 

 most complex mosaic of parts differing chemically and physi- 

 cally. Each of these parts has its individual characters — its 

 own climate, in the widest sense. Kraus emphasizes the 

 importance of the structure of the substratum, upon which 

 depend the water-content and the temperature, and which 

 determines above all else the nature of the habitat. .Among 

 other interesting observations, he points out. as illustrating 

 the dependence of air temperature upon soil temperature, that 

 the temperature is highest at the surface of the soil, and that 

 from this point it diminishes during the day both above and 

 below, while at night it increases upwards and downwards. 



KOOT-XODULES IN NON-LEGUMINOUS PLANTS. 

 — Two interesting papers on the structure of bacterial root- 

 nodules in plants not belonging to the family Leguminosae 

 (in which such nodules are apparently always found) are 

 published in i\\c Annals of Botany (XX\T. January, 1912) one 

 by Professor Bottomley on the nodules of bog myrtle (Myrica 

 jialc), and the other by Miss Spratt on those of an alder 

 i.-I/hks incana) and two species of Elaeaguus (B. edulis and 

 R. rhainnoidcs). 



In Myrica the root-nodules are modified lateral roots. The 

 young primary nodules give rise, by branching, to the character- 

 istic cluster-nodules, surrounded by rootlets w-hich grow out 

 through the end of each branch; three branches or secondary 

 nodules arise from the end of each primary nodule, and like 

 it are modified lateral roots; then the central cylinder of the 

 primary nodule elongates and grows through the apex of the 

 nodule, giving rise to the hair-like rootlet. In each mature 

 nodule four zones can be distinguished : (1 ) the apical meristem ; 

 (2) the infection-thread area; (3) the b.icterial zone, which 

 includes most of the cortical tissue of the nodule, and consists 

 chiefly of the enlarged cells containing bacteria ; (4) the basal 

 zone — the lower end of the nodule, devoid of bacterial cells, 

 but containing numerous cells filled with oil-drops. After the 



