55« 



NATURE 



[September 26, 1907 



'■merits of modern ferns, and was led to the unexpected 



,ult that the "pits" are really quite open, placing the 

 Luvities of adjacent elements in free communication, while 

 the pits themselves communicate with one another in the 

 thickness of the wall, a " pit-closing- membrane " being 

 tjuite absent. In other words, the wall of the typical 

 xylem element of a fern consists of corner columns joined 

 by pairs of separate horizontal bars. In development the 

 corner columns and bars are gradually lignified, while 

 the pectic substance forming the rest of the primitive wall 

 becomes granular and disappears. In Pteris aquilina the 

 substance joining the two bars of each pair remains, 

 though the pits themselves are open. The author exhibited 

 preparations fully demonstrating the facts described in his 

 paper. 



Prof. F. W. Oliver read a paper on the structure and 

 affinities of Physosioma elegans (Williamson), a pterido- 

 spermous seed from the Coal-measures, in which he gave 

 a full description of the seed in question. Williamson 

 afterwards called it I.agcnosloma physoides, and it is 

 certainly closely allied to the Lagenostomas. Neverthe- 

 less, it possesses certain curious and unique features which 

 well warrant its separation, and lead to the conclusion 

 that it represents one of the most primitive types of 

 pteridospermous seed as yet discovered. 



Mr. D. M. S. Watson described the cone of Botbro- 

 dendron (Lepidodendron) niundujn as practically a Lepido- 

 strobus with the radial extension of the sporophylls very 

 much reduced, a state of things that would be expected 

 from a consideration of the vegetative organs. It appeared 

 that there had been a confusion with Miadesmia, the 

 block containing the latter plant also having fragments 

 of two other Lycopod cones, of which this is one. The 

 idea of an immediate connection with -Spencerites must 

 be given up. In the course of the discussion Prof. Weiss 

 remarked that we now know Bothrodendron more com- 

 pletely than any other fossil Lycopod. 



Papers on Schizophyta. 



Mr. David Ellis read a paper on the phylogenetic con- 

 nections of the recent addition to the thread-bacteria, 

 Spirophyllum fcrrugineum, Ellis, in which he showed that 

 the new species links the iron-bacteria with the genus 

 Spiromonas, and suggested that the definition of Migula's 

 order Chlamydobacteriacea; should be modified so as to 

 include both of these genera. 



Mr. B. H. Bentley read a paper, on cell-division in 

 Merismopedia, in which he described a process like 

 karyokinesis in the cells of this genus. The paper was 

 somewhat adversely criticised by Mr. Wager. 



Ecological Papers. 



Prof. Vapp communicated a paper by Prof. H. H. W. 

 Pearson (Cape Town) describing a botanical excursion to 

 the Welwitschia desert. The conditions obtaining in this 

 desert (German South-West Africa) are remarkably severe 

 — the annual rainfall varies from zero to 3 cm., the 

 illumination is very intense, and surface deposits of salt- 

 petre and other salts are frequent. This severity of con- 

 ditions, which must affect the germination of seedlings, 

 results in an extreme paucity of vegetation. One may 

 sometimes walk for miles without seeing a single flower- 

 ing plant, while as regards species, in the British terri- 

 tory of Walfisch Bay, the total phanerogamic flora, ex- 

 cluding that of the Khusib river-bed, probably docs not 

 number more than twelve species. Welwitschia itself has 

 a range extending from 14° to 23° S. latitude. It seems 

 to prefer more or less sheltered and sloping valleys at an 

 elevation of about 100 feet above sea-level. The author 

 gave some interesting observations respecting the pollin- 

 ation of Welwitschia, adducing evidence to show that it 

 is largely effected through the agency of a parasitic hemi- 

 pterous insect (Odontopus), which is apparently never 

 absent from the plant. 



By^ comparing the Welwitschia plants of known age 

 at Kew with the youngest seen in Damaraland, Prof. 

 Pearson estimates that the latter cannot be less than forty 

 to fifty years old. From this it follows that the con- 

 ditions necessary for the successful germination of the 

 seeds of Welwitschia occur but rarelv. As there are not 

 wanting indications that the rainfall of this area was once 



NO. 1978, VOL 76] 



considerably in excess of the present one, it is to be 

 feared that the effective reproduction of Welwitschia is 

 now more rare than formerly, and that, with the con- 

 tinuance of the climatic conditions at present prevailing in 

 western Damaraland, the species is doomed to become 

 extinct in its native region. 



Prof. R. H. Yapp gave a paper on the hairiness of 

 certain marsh plants. A considerable number of plants 

 found in damp or marshy habitats possess a more or less 

 dense covering of hairs. Many of these plants, however, 

 show seasonal differences in respect of hairiness. Thus 

 the leaves formed in spring on low-growing shoots are 

 usually small and glabrous, while the later leaves, 

 especially those on the erect flowering shoots, are larger, 

 and increasingly hairy. Spiraea Ulmaria was referred to- 

 in some detail. In spring this species successively forms 

 glabrous, partly hairy and densely hairy leaves. The 

 partly hairy leaves show a regular distribution of the 

 tomentum on their lower surfaces, the leaves decreasing 

 in hairiness from above downwards, while the margins 

 are generally more hairy than the central parts of the 

 lamina. This distribution of hairs is suggestive, in view 

 of the fact that if Spiraea ulmaria, var. demidata, an 

 entirely hairless variety, be grown in an exposed situ- 

 ation, its leaves suffer more than those of the hairy 

 form, and that the withering due to exposure first begins 

 in those parts of the leaf which, in the hairy variety, are 

 the first to be covered with the tomentum. 



Other Papers. 



Mr. R. P. Gregory read a paper on the inheritance of 

 certain characters in Primula sinensis, in which he dealt 

 with experiments on the inheritance of long and short 

 styles, leaf form, colour of stems and petioles, and, lastly, 

 of flower colour. While some of these characters obey 

 simple Mendelian rules, the colour inheritance presents 

 very complex problem? which are by no means completely 

 elucidated. Two distinct classes of whites in flower colour 

 were separated. Sutton's " Snowdrift," with pure green 

 stems, is a true albino, but in all the other races of white- 

 flowered plants a character occurs which inhibits the 

 development in the flower of a colour potentially present 

 in the plant. The results of crossing these " dominant 

 whites " with coloured flowers are complex. Various 

 partial explanations of the observed results were suggested 

 by the author. 



Local Papers. — A paper on Charnwood Forest, illus- 

 trated by particularly beautiful lantern-slides, was read 

 by Mr. W. Bell, the local secretary, in which the scenery 

 and vegetation of the forest were treated descriptively and 

 historically, and by a comparison of old lists of species 

 with those found at the present day the effect of drainage 

 and cultivation on the native flora was brought out. 



Mr. .'\. R. Horwood read a paper on the disappearance 

 of certain cryptogamic plants from Charnwood Forest 

 within historic times. In this paper the great impoverish- 

 ment of the lichen flora was particularly noticed, and was 

 attributed largely to the effect of smoke, a similar pheno- 

 menon to that observed in the region affected by the 

 Lancashire and Yorkshire smoke-cloud. 



Semi-popular Lecture. — Prof. Weiss delivered the semi- 

 popular lecture on " .Some .Advances in our Knowledge of 

 the Pollination of Flowers." The lecturer dealt with the 

 newer work on this subject, and discussed its bearing 

 upon the older views of the mechanisms of pollination. 



Exctirsions. 

 By invitation of Mr. C. C. Hurst, an excursion (in con- 

 junction with Section D) took place to Burbage to examine 

 the results of his experiments on Mendelian heredity in 

 rabbits, sweet-peas, S:c., and also to witness a demonstra- 

 tion of the inheritance of eye-colour in man, for which 

 about 100 school children from the families studied by 

 Mr. Hurst were assembled. Most unfortunately, rain to- 

 some extent interfered with the success of these extremely 

 interesting demonstrations, but Mr. Hurst very kindly_ re- 

 peated them in Section D at a later period of the meeting. 

 The allelomorphic pair of characters in eye-colour studied 

 bv Mr. Hurst are the presence or absence of "brown pig- 

 ment on the front of the iris. Eves with the former 



