440 



KNOWLEDGE. 



November, 1911. 



the actual site of 



Dr. Gordon's views of thermal pool; 

 petrifaction. 



PAPERS OX FLXGI AND BACTERIA.— Mr. A. S. 

 Home described the nuclear divisions which occur in a Fungus 

 parasitic on the Potato, Spoiigospora sulani, a member of 

 the lowly group Plasmodiophoraceae. Several other genera 

 of this group were also dealt with by Mr. T. G. B. Osborn in 

 a paper entitled, " The Life Cycle and Affinities of the 

 Plasmodiophoraceae." Without entering into the technical 

 details of nuclear division described in these papers, it may 

 be stated that the observations made tend to strengthen the 

 suggested relationship of this group to the Slime-Fungi 

 (My.xomycetesl and possibly also with the Chytridiaceae. In 

 Spoiigospora solan i. Home describes a very curious form of 

 nuclear division, in which four loop-like chromosomes appears 

 and later join end to end to form an equatorial ring around 

 the nucleolus ; this ring divides into two daughter rings, each 

 of which finally breaks up again into four chromosomes, while 

 the nucleolus constricts to form two daughter nucleoli. 



Professor Bottomley described the structure and function 

 of the root-nodules of the bog myrtle (Myrica gale) which 

 are formed as modifications of normal lateral roots, these 

 branching and forming clusters covered with rootlets growing 

 out through the end of each nodule or branch — the branching 

 is due to the outgrowth of lateral roots, and not to forking 

 of the apex of the primary nodule, as in the nodules of Cycas, 

 Alder and Elacagnus. The cortex of a young nodule contains 

 (a) numerous cells with bacteria, and (6) cells filled with oil 

 drops : towards the apex of the nodule the infection threads can 

 be seen passing from cell to cell, and the whole nodule is covered 

 by two or three layers of cork cells. Pure cultures of the 

 bacteria show small rod-like bodies resembling Pseudoiuonas 

 radicicola. the organism found in all Leguminous nodules, 

 and giving a definite fixation of nitrogen when grown in flasks. 

 Voung Myrica plants grown in pots in soil deficient in nitrogen 

 flourished well if possessing nodules ; if without nodules on 

 their roots they soon died. I-'xidently the nodules of Myrica 

 are concerned with the assimilation of atmospheric nitrogen, 

 as are the root-nodules of Cycas. Alder, Elacagniis and 

 Podocarpns, the other known genera of plants outside of the 

 Leguminosae which have root-nodules. 



PAPERS ON PHYSIOLOGY. — Professor Bottomley 

 described " Some Effects of Bacteriotoxius on the Germination 

 and Growth of Plants," illustrated by some remarkable photo- 

 graphs of comparative cultures. An aqueous extract of well 

 rotted manure or fertile soil, obtained by treating one hundred 

 grammes of manure or soil with five hundred cubic 

 centimetres of isotonic salt solution and filtering through 

 a Pukall filter, has an injurious effect on the germina- 

 tion of seeds and their further growth in sand, even 

 when supplied with normal food solution. This inhibitory 

 effect of the extract can be destroyed by boiling. The harm- 

 ful effect is due to the presence of certain bacteriotoxius, 

 probably of the nature of toxalbumoses, formed by the activities 

 of the decomposition and denitrifying bacteria in the manure 

 or the soil, and by heating the toxic influence is destroyed and 

 the substance rendered available as a nutrient. 



Experiments with germinating seeds of mustard, turnip, 

 tares, and barley gi\e support to this theory. Seeds 

 germinated in pots containing sand moistened with (rt) 

 distilled water, (h) saline solution, (c) raw extract, Irf) boiled 

 extract, showed that the raw extract almost prevented 

 germination and the subsequent growth was very feeble, 

 whilst the boiled extract, although slightly retarding 

 germination at first, soon appeared to benefit the seedlings 

 which became stronger and healthier than those grown with- 

 out extract. The extract was also found to have a marked 

 influence on the growth of certain soil organisms. It 

 stimulated the growth of denitrifying bacteria, and inhibited 

 the growth of the nitrogen-fixing bacteria. Both these eftccts 

 were destroyed by boiling the extract. 



Mr. S. Mangham, who has already done useful and interest- 

 ing work on the translocation of carbohydrates in plants, 

 described some of his observations on the presence of sugar 



in the tissues of the Sea Tangle, Lain in aria. The two 

 species L. digitata and L. saccharina were examined for 

 sugars at various times of year by means of Senft's method of 

 forming osazones. Observations were made upon sections 

 cut from the stipe, the region of new growth, and from the 

 lamina. Crystalline osazones have been found in the cortical 

 cells, the sieve-tubes, and the hyphae in both species, and 

 particularly at the time of formation of the new lamina in 

 L. digitata. Some of the crystals in the latter plant very 

 closely resemble those yielded by maltose, but their exact 

 identity is at present unknown. This production of osazones 

 in the hyphae and in the sieve-tubes after treatment with 

 Senft's reagent aflVirds experimental evidence in support of the 

 conducting and storing function hitherto assigned to these 

 elements mainly on account of their structure. 



Miss Eraser described in detail " The Longitudinal Fission 

 of the Meiotic Chromosomes in Vicia Paha." 



Dr. A. .A.. Lawson, in a paper on " Nuclear Osmosis as a 

 Factor in Mitosis," put forward views which run counter to 

 some generally accepted interpretations of the phenomena of 

 nuclear division, and which are likely to lead to further 

 discussion. Dr. Lawson claims to have discovered that the 

 nuclear membrane does not break down or collapse at anv 

 period, but behaves as one would expect a permeable plasmatic 

 membrane to behave under varying osmotic conditions ; and that 

 the achromatic spindle can no longer be regarded as an active 

 factor in mitosis, but is simply the passive eflect or expression 

 of a state of tension set up in the cytoplasm and caused in the 

 first place by nuclear osmotic changes. 



Miss L. Digby gave a preliminary account of the cytology 

 of the hybrid Primula Icewcnsis, its parents, and the ensuing 

 generation. The original P. kezcensis appeared in a pure batch 

 of P. floribunda seedlings at Kew in 1899, and proved to be 

 a cross between P. floribunda and P. vcrticillata. The 

 hybrid was sterile, with only thrum-eyed flowers, but some 

 years later a single pin-eyed flower was noticed in Veitch's 

 nurseries. This was promptly fertilised, good seed was set, 

 and the resulting plants had both pin-eyed and thrum-eyed 

 flowers and were fertile. Thus the whole fertile or seedling 

 stock of P. heu'cnsis owes its origin to the one pin-eyed flower 

 on the sterile or type stock of P. keiccnsis. 



The parents of P. keiccnsis (sterile) have identically the 

 same number of chromosomes, and (as might be expected) this 

 number is repeated in the hybrid : P. floribunda, P. verti- 

 cillafa. and P. keiccnsis (sterile) all have eighteen (2x) and 

 nine (x) chromosomes. The surprising phenomenon occurs 

 in the seedling P. keiccnsis, in which there are thirty-six (2x) 

 and eighteen (xl chromosomes. By some means either at, or 

 subsequent to, the fertilisation of the pin-eyed flower on the 

 sterile stock the number of chromosomes has been duplicated : 

 this doubled number is continued throughout the generations 

 of the fertile P. keiccnsis, and is also characteristic of the 

 variety P. kewensis farinosa. This increase cannot be 

 accounted for by apogamy ; the divisions in the embryo sac 

 mother nuclei of both sterile and fertile forms are normal, 

 and in the one case nine (x) and in the other eighteen (x) chro- 

 mosomes are seen at meiosis, while in the surrounding tissue 

 there are correspondingly eighteen (2x) and thirty-six (2x) 

 chromosomes. The doubled number of chromosomes has 

 since re-appeared in a cross made in 1910, at Kew between 

 P. floribunda var. isabcllina and P. vcrticillata ; the 

 resulting hybrids not only resemble P. kewensis farinosa in 

 external features, but also possess thirty-six (2x) chromosomes. 



This remarkable sudden duplication of chromosomes has 

 its counterpart in the Oenotheras. Oc. Laniarckiana has 

 fourteen (2x) and seven (x), while Oc. gigas which mutated 

 from Oc. Laniarckiana has twenty-eight and fourteen. Like 

 the fertile P. keiccnsis, Oc. gigas has again arisen from two 

 sources — once as a hybrid and once from a pure strain of 

 Oc. sublinervis. In the Oenotheras, as there is no evidence 

 of the addition of new unit characters, the doubling of the 

 chromosomes is believed to be brought about by longitudinal 

 fission. In the Primulas the phenomenon is apparently 

 associated with the change from the sterile to the fertile 

 condition. 



