380 SECTIONAL TRANSACTIONS.— K. 



Little is known of the British species since the work of Griiber on the mode of 

 branching of the shoot, and of Nienburg on the development of the conceptacle. 



Observations have been made from living plants and from material preserved 

 in situ at different times of the year. 



The development of the conceptacle from a single initial cell is shown, and the 

 retention of a single basal hair up to the time of formation of antheridia is a con- 

 spicuous feature of the young conceptacle. The production of antheridia and oogonia 

 is described, and the formation of ' plugs ' at the mouths of old conceptacles reported 

 — a phenomenon similar to that described by Tahara for Sargassum Horneri. 



The genus as a whole is characterised by marked vegetative activity, new fronds 

 arising from the rhizome and, especially in B. levigata, by proliferation from the 

 bases of old stipes. The anatomy of the stipe is described for the three species ; 

 in B. tuberculata the anatomical relationship to the other genera of the group Cystosiro- 

 Sargasseae is evident, while this is less clear in the two South African species. 



Mr. W. T. Mathias. — The Cytology of Callithamnion, 



The paper deals primarily with the stages of nuclear division undergone during 

 the development of the tetraspores of Callithamnion brachiatum. The resting nucleus 

 is described and the stage where synapsis occurs is indicated. The various steps in 

 division are unlike those described for other red algae, and the diploid chromosome 

 number is 18-20, in the tetraspore mother cell, this number being reduced to 9-10 

 in the mature tetraspore. 



The development of the spermatia in this species is also described, and the nucleus 

 of the mature spermatium is shown to be a homogeneous hollow band of chromatin 

 encircling the cell, and not a granulated network as it has been described. 



The cytology of abnormalities in Callithamnion tetragonum is also traced, and 

 shows that tetraspores borne on sexual plants develop and mature, while the 

 carpospores possess the Haploid chromosome number, suggesting cytological insta- 

 bility, and a more complicated alternation of generations. 



Mr. A. Malins Smith. — The Algce of a Boy : Five Years' Observations. 



The algae of a small sphagnum bog have been examined, approximately monthly, 

 for five years. Records of temperature and hydrogen-ion concentration of the water, 

 as well as observations of the weather conditions and of the flow of the water, have 

 been periodically taken. Chemical analyses of the water have also been made. The 

 results shed light upon the specific composition of the alga-flora of such waters, the 

 relative abundance and interdependence of the chief groups of algae, and the periodicity 

 of the various species. The relation of the alga-flora to the phanerogamic flora is 

 briefly considered, and the status of the upland sphagnum bog as a habitat for a 

 definite algal association is estimated. Comparison is made with the alga-flora of 

 lowland pools and montane lakes. 



Prof. N. E. Svedelitjs. — The Cytology and Development of Asparagopsis 

 armata. 



The general morphology of this alga has already been described by Conolly. 

 Observations now have been made especially regarding the cytology and the develop- 

 ment of the cystocarp. Tetraspores are not known. The carpogonial branch is 

 3-celled, just as in Bonnemaisonia. The carpogonium at an early stage is binucleate, 

 as in most Florideae. Spermatia are to be seen adhering to the trichogyne and also 

 inside them. Fertilisation thus certainly occurs. The number of chromosomes in 

 the spermatia is at the most ten. Seven to eight have been observed with certainty ; 

 but probably there are some more. To determine the number exactly is very difficult 

 owing to the smallness of the nuclei. The haploid chromosome number is then at 

 most ten. 



The carpospores are not produced as directly as in Bonnemaisonia, since the 

 sporogenous filaments branch and in the first place form an extensive tissue, a so-called 

 ' nucleus,' from which later on the carpospores are formed. 



In the mitoses in the young sporogenous filaments a chromosome number of 

 about eight has been observed. Thus the carpospores also must be haploid. 

 Asparaqopsis, then, is certainly a haplobiontic alga. 



