October 28, 1909] 



NA TURE 



537 



BOTANY AT THE BRITISH ASSOCIATION. 

 CO far as Section K is concerned, the Winnipeg meet- 

 •~^ ing must be pronounced to have been a distinct 

 success. Though less than a dozen British botanists and 

 only one Canadian were present, the numbers attending 

 the section were about up to the average. This was largely 

 due to the presence of a number of American botanists, 

 many of whom communicated papers and in other ways 

 contributed to the success of the meeting. 



The opening address of the president, Lieut. -Colonel 

 Prain, was delivered on Thursday, August 26. It dealt 

 chiefly with the position of modern systematic botany, and 

 its relations to pala;obotany, phytogeography, and other 

 branches of botanical study. The address was published in 

 full in Nature of September 50. 



The papers read during the meeting may be roughly 

 classified according to subjects. 



Cytological and Fungal Papers. 



Prof. J. B. Overton tof Wisconsin) contributed a paper 

 on the organisation and reconstruction of the nuclei in the 

 root-tips of PodophyUum peltatum. After summarising the 

 work of Gregoire and others, the author described his own 

 observations, which, in his opinion, strongly support the 

 view of the individuality of the chromosomes. During the 

 passage of the chromosomes from the equatorial plate to 

 the poles, they e.xhibit progressive vacuolisation. Dr. 

 Overton believes that each individual chromosome increases 

 in size, and ultimately forms an independent elementary 

 reticulum. Thus the reticulum of the resting nucleus is 

 composed of a number of these smaller reticula. Con- 

 versely, during the earlier prophases of division, the 

 chromosomes become more condensed and distinct, and, 

 joining end to end, give rise to the well-known spireme. 



Mr. Harold Wager communicated a paper by Miss A. 

 Peniston and himself on the nucleus of the yeast plant. 

 The authors contend that the so-called vacuole of the yeast 

 cell is in reality part of the nuclear apparatus. This 

 vacuole is surrounded by a peripheral chromatin network, 

 which in its turn is connected with a stainable nucleolus. 

 The paper was illustrated by a number of convincing draw- 

 ings. 



Miss M. C. I. Fraser discussed the nuclear phenomena 

 of Ascomycetes in relation to heredity. Fertilisation in the 

 Ascomycetes may be either normal or degenerate. The 

 latter, which consists of the fusion in pairs of either 

 ascogonial or even vegetative nuclei, is found in cases 

 where one or both sexual organs are absent. Fertilisation 

 of either type is followed by a second nuclear fusion in the 

 ascus. The sexual fusion is compensated by a true meiotic 

 reduction, while the fusion in the ascus is followed by a 

 simpler brachymeiotic division. It thus appears possible 

 to differentiate between sexual and asexual fusion by a 

 study of the subsequent reduction phenomena. 



Prof. .'\. H. R. Buller (of Winnipeg) gave an account 

 of the production and dispersion of spores in the Hymeno- 

 mvcetes. .\ number of experiments were made on the rate 

 of spore discharge, the path of the falling spores, &c. 

 During the paper Prof. Buller gave a pretty demonstra- 

 tion of the discharge of spores from the fruit-body of a 

 species of Polyporus. By suspending the fungus in a 

 closed glass chamber, through which a concentrated beam 

 of light was passed, the clouds of falling spores were 

 rendered clearly visible. A full account of this work is 

 contained in the book on fungal researches just published 

 by the author. 



Another paper by Prof. Buller, in collaboration with Mr. 

 C. W. Lowe, dealt with the number of bacteria in the air 

 of Winnipeg. Observations were made on the University 

 campus every week for a year. Both the volumetric and 

 the plate methods were employed. During the winter half 

 of the year the average number of micro-organisms in 

 ten litres of air was oq, while in the corresponding summer 

 half I he average number rose to 10-33. 



Papers on Flcridopliyta. 



Prof. D. H. Campbell (Leiand Stanford University) read 

 a paper on the prothallium and embryo sporophyte of 

 Danjea, a fine series of which (belonging to several species) 

 had been procured in Jamaica. Of the points described by 



NO. 2087. VOL. 81] 



the author, two may be mentioned. First, as compared 

 with other MarattiaceiE, the ventral canal cell of the 

 archegonium is very imperfectly developed. Secondly, no 

 trace of a root can be found until the embryo has reached 

 a considerable size. The first root then arises endo- 

 genously. 



Prof. D. T. Gwynne-Vaughan communicated a paper 

 by Dr. Kidston and himself on the ancestry of the 

 Osmundaceae. Lalesskya and Thamnopteris are two genera 

 of primitive Osmundacea; from the Permian deposits of 

 Russia. The stem in these forms contains a protostele 

 with a solid mass of xylem. The latter, however, is not 

 homogeneous, as it consists of a central mass of short 

 tracheids surrounded by a peripheral zone of normal scalari- 

 form tracheids. This central mass of short tracheids is 

 held by the authors to be homologous with the paren- 

 chymatous pith of the modern Osmundaceae. They also 

 believe that the Osmundaceae and Zygopterideae have been 

 derived from a common ancestor. 



A paper was also presented by Mr. W. T. Gordon on 

 the structure of a new Zygopteris. This species (Z. Petty- 

 curensis) exhibits a protostele, a type of vascular system 

 which had hitherto not been found in the group. This 

 form thus occupies the same position in the Zygopterideae 

 as Thamnopteris schlechtendahlii does in the Osmundaceae. 



Ecological Papers. 



F'riday morning was largely devoted to the consideration 

 of papers on ecology. The first was by Prof. H. C. 

 Cowles, of Chicago, on the fundamental causes of 

 succession among plant-associations. In dealing with the 

 fact of succession. Prof. Cowles stated that plant- 

 associations only exhibit this phenomenon when changes 

 occur in the external conditions ; but complete stability of 

 conditions is rarely met with, so succession constitutes the 

 normal course of events. The earlier stages may be 

 termed the proximate, and the later ones the ultimate 

 stages. Except in those cases where the proximate and 

 ultimate formations are the same, as, for instance, in 

 deserts, it is only in the ultimate stages that a plant- 

 association becomes relatively stable. The author then 

 discussed a number of the causes of succession. Apart 

 from such obvious ones as topographic and climatic 

 changes, the most important are those which are more or 

 less associated with the plants themselves. Of these, Dr. 

 Cowles laid especial stress on two factors : the accumula- 

 tion of humus, which involves changes in the temperature, 

 and the moisture and air content of the soil ; and the 

 increase of shade, due to the increasing luxuriance of the 

 vegetation. The ultimate formation of any upland will be 

 composed of plants that can germinate in the densest shade 

 that exists there. Other factors discussed were the 

 invasion of an area by alien species, and the influence of 

 man. The latter makes itself felt chiefly by reason of 

 man's destructive activity. Speaking broadly, the eiTect of 

 interference by man is to keep plant-associations more 

 xerophytic than they would otherwise be. 



Prof. F. Ramaley (Colorado) discussed the Rocky Moun- 

 tain flora in relation to climate. He stated that the flora 

 of the Rockies is remarkably uniform from Canada to 

 Colorado ; but any given species must be looked for at 

 higher and higher altitudes as one travels southwards from 

 Canada. The author is of opinion that the chief factor 

 which determines this altitudinal distribution is tempera- 

 ture. This he regards as more important in this instance 

 than either topography, soil, or rainfall. 



Prof. B. E. Livingston (Baltimore) then gave an account 

 of the porous cup atmometer as an instrument for 

 ecological research. The author first emphasised the 

 importance of evaporation determinations in _ ecological 

 investigations, and then described the form of instrument 

 he has himself used. Finally, he gave some useful hints 

 with respect to precautions to be observed when using this 

 instrument. 



Prof. R. H. Yanp gave the result of some observations 

 and experiments on the ecology of Spiraea Ulmaria. This 

 plant exhibits curious seasonal changes in respect to the 

 formation of glabrous and hairy leaves. It was shown 

 that the production of these two types of leaves in nature 

 varies with the annual march of evaporation and light 

 intensitv. 



