406 SECTIONAL TRANSACTIONS.— K. 



Nuclear division is mitotic, all the nuclei within the same individual dividing 

 simultaneously. The nucleus of the host cell is found associated with the parasite, 

 and generally appears unhealthy. When mature the whole of the soma divides up 

 into a large number of uninucleated zoospores which escape by the bursting of the cyst 

 wall. They are able to penetrate the wall of the host cell, and then either make their 

 way out of the root or enter another cell, where they pass through the same cycle. 



No apparent pathological effect is produced in the host, and there are no external 

 signs to indicate that a plant is attacked by the fungus. 



The parasite is considered to belong to the Chytridiales, and is probably allied to 

 Catenaria or Hyphochytrium. 



Prof. Dame Helen Gwynne-Vaughan, G.B.E., and Mrs. H. S. 

 Williamson. — A Reinvestigation of the Life-history of Pyronema 

 confltiens. 



Pyronema conftuens fruits readily in single spore culture, the fertile hyphae branch 

 dichotomously, antheridia pushing in among the paired oogonia. The young 

 trichogyne is cut off by a wall ; this opens for a brief period, allowing the male nuclei 

 to enter the oogonium, and is then closed. As first observed by Harper, the sexual 

 nuclei fuse in pairs in the oogonium. The j'oung ascogenous hyphse lack septa ; 

 below the asci, after di^^sions have occurred, manj' of the cells contain two nuclei. 

 The divisions in the sheath and paraphyses show six chromosomes, those in the 

 ascogenous hyphse twelve. As recorded by Claussen, the first divisions in the ascus 

 are meiotic, showing twelve gemini. In the third telophase six chromosomes only 

 are seen. 



Dr. B. Barnes. — On Variations in Fungi induced by heating the Spores. 



Spores of Eiirolium herbariorum, Botrytis cinerea and Thamnidium elegans, taken 

 from strains known to be constant under ordinary conditions of culture, have yielded 

 variant forms after exposure for a short time to high temperatures. The more 

 extreme variants appear to be permanent ; less marked variants have tended to 

 revert to the normal form. 



The behaviour of the permanent variants suggests that they are less vigorous 

 than the normal strains. Some are of weak growth, some stale with great readiness, 

 and some form scanty crops of spores, or fail to develop all the stages shown by control 

 cultures. 



Comparable results have been obtained by other workers bj^ the application of 

 heat to higher plants and to insects. 



Miss H. Heslop Harrison. — The Cytology of the Genus Euphorbia. 



The root-tips of seventeen species of Euphorbia have been examined. These 

 species may be arranged in two series according to their chromosome number. In 

 the first are four species, three having a diploid chromosome number of 20 and one 

 of 40. In the second are thirteen species, three having 12 somatic chromosomes, 

 six having 18, one having 30, two having 36 and one having 42. Those species with 

 18, 30, 36 and 42 chromosomes possibly form a true polyploid series based on three. 

 In two species, E. terracina and E. Welwitschii tetraploid tissue has been found. 

 In the latter case this has arisen by the fusion of the two nuclei in binucleate cells. 

 Chromosome shape has been found to vary considerably from tissue to tissue. 

 This is very clearly shown in E. verrnccsa and E. terracina, where the plerome chromo- 

 somes are so contracted as to become almost unrecognisable- 

 Distinct evidences of chromosome fragmentation have been found in two species — 

 E. capitata and E. caput- Medusce. 



In several species the chromosomes on the metaphase plate are arranged in pairs, 

 the members of each pair being obviously corresponding maternal and paternal 

 chromosomes. In many cases distinct chromatin connections are seen between them. 



Afternoon. 

 Excursion to Potterne. 



Excursion to Portishead Marshes. 



