SECTIONAL TRANSACTIONS.—K. 491 
Wednesday, September 30. 
Miss B. D. Grecory and Prof. L. Newron.—Fwurther Light on the Life 
Histories of Gymnogongrus Griffithsiae and Ahnfeldtia plicata. 
Mr. R. E. Harries and Mr. G. Bessincton.—further results in Cultural 
Work on Laminaria. 
Miss E. M. Linp.—The Life History and Cytology of two species of Ulothriz. 
Until recently it was considered that individual plants of all the Chlorophyceae 
were haploid. During the last five years an alternation of haploid and diploid phase 
has been demonstrated in several genera. A study of two species of Ulothrix was 
undertaken in order to investigate the nuclear changes in the life cycle. 
The two species described—Ulothrix zonata and Ulothrix rorida—were found 
growing mixed together. As much attention has already been devoted to U. zonata 
by previous workers, the only points discussed in this paper with regard to this species 
are those upon which there is still some difference of opinion. The existence of 
microspores has recently been doubted. These are described, and also a form of 
_ vegetative reproduction by fragmentation and a hitherto undescribed branching of 
the filaments. ‘The variation shown by this alga under different conditions of 
environment is emphasised. 
Ulothrix rorida (Thuret) is considered to be a form described by Thuret in 1850 
but not since included in systematic works on the Chlorophyceae. It is distinguished 
from U. zonata by the smaller average size of its filaments, the possession of only one 
pyrenoid per cell and by its spindle-shaped zoospores. This species begins to develop 
in October, reaches a maximum in February and then decreases rapidly. It produces 
zoospores throughout the autumn and winter, but in March each year there appear 
very numerous strongly coiled gamete-forming filaments. Gamete production 
coincides with low temperature, bright sunshine and low pH, and is followed by the 
death of the filaments. The change from zoospore to gamete formation is very 
sudden, and is conditioned by the environment rather than by the nature of the 
filament. 
All filaments are haploid, and no reduction division can be demonstrated in the 
formation of any of the reproductive cells. The germination of the zygote has not 
yet been studied beyond an early stage, but it is suggested that here, as in Ulothrix 
zonata, the zygote represents the only diploid phase in the life-cycle. 
Mr. F. W. Jane.—Chromosome Studies in the Hypoxidoidee. 
Diploid nuclei of six genera of the Hypoxidoidew have been studied, and the 
variety of chromosome form occurring in this section of the Amaryllidacee is discussed. 
In Hypoxis the chromosomes are small and numerous, ranging in number from 
about forty to ninety in different species. In Cuwrculigo recurvata, where there are 
eighteen chromosomes, and in Tecopnilea cyanocrucus and T. violacea, where there 
are twenty-four, the chromosomes are very small, and little success attends any effort 
to elucidate their structure. 
The chromosomes of Anigozanthos flavida and A. rufa are larger and number 
twelve. These, together with the large chromosomes of Bomarea (18) and Alstremeria 
(16) yield material in which details of chromosome structure are more easily seen. 
The occurrence of chromonemata is described. In Bomarea an endogenous spiral 
or zig-zag thread is visible in anaphase chromosomes, and comparable threads occur 
in prophase nuclei of plants of this genus and Alstremeria. In Alstremeria at 
metaphase paired chromomeres are visible in each daughter segment of the splitting 
chromosomes. Constrictions and spindle fibre attachments are also described. 
Miss HeLtena Hestop Harrison.—Further Studies in the Chromosome 
‘Number and Morphology of the Genus Euphorbia. 
In an effort to trace the correlation between chromosome number and morphology 
in this genus and phylogenetic relationship, the cytology of fifty species has been 
studied. In every case material for examination was provided by the root tips of 
