80 SUMMARY OF CURRENT RESEARCHES RELATING TO 



species. The flat or round always erect thallus has a regular dicho- 

 tomous branching ; the basal portion or stipe differs in form and struc- 

 ture from the rest of the thallus. The growing point is very uniform 

 in structure throughout the genus, and is composed of a mass of densely 

 interwoven hyphse. 



Carpogones in a rudimentary condition were found only in one 

 species ; but ripe cystocarps were not infrequently obtained, though in 

 comparatively few species. Antherids were met with frequently, always 

 in separate individuals, the appearance of the male organs resembling 

 that of the male conceptacles of Fucus. The tetrasporanges are, at 

 present, of much greater use in characterising the species. The 

 assimilating tissue consists (in G. Diesingiana) of two or three layers 

 of cells, covered by short, unbranched, club-shaped shoots. From the 

 terminal cells of these shoots spring two-celled filaments, the upper cell 

 of which, dividing crucially, becomes a tetrasporange. In G. striata 

 the stalk of the sporange consists from the first of a number of cells. 

 Proliferation is common. 



The numerous species are classified under nine sections, and the 

 specific characters and relations of the sections to one another are dis- 

 cussed in detail. 



Abnormal Conjugation in Spirogyra.* — Dr. L. Montemartini re- 

 gards the mode of conjugation in Spirogyra as exhibiting an advance on 

 that in the Desmidieae, where there is no differentiation between the 

 conjugating cells; Mesocarpm, where conjugation takes place in the 

 canal which unites the two conjugating cells, presenting an intermediate 

 stage. He records instances of abnormal conjugation in different species 

 of Spirogyra, some of which correspond to abnormalities frequently 

 met with in flowering plants : — conjugation between three cells ; poly- 

 gamy and polyandry ; parthenospory ; and hermaphroditism. 



Chromatophores of Fresh-water Diatoms, f — Emma Ott has ex- 

 amined in detail the structure, arrangement, and mode of division of 

 the chromatophores in a number of genera and species of fresh-water 

 diatoms. The following are the more important new observations. 



In all the genera which have two chromatophores (Fragilaria, 

 Synedra, Eunotia, Pleurosigma, Navicula, Pinnularia) a transverse septa- 

 tion is the most essential factor in the process of division, viz. at right 

 angles to the longer diameter. A transverse division was established 

 by the authoress for the first time in Navicula and Pinnularia. In 

 Nitzschia, although it has two chromatophores, the fission is longi- 

 tudinal ; but the formation of the new cell-wall begins even here in 

 the middle. In genera with only one chromatophore, longitudinal 

 fission has the greatest influence in the process of division. The 

 formation of the new cell-walls causes the chromatophore to be pushed 

 aside. 



The following is suggested as a classification of the genera of fresh- 

 water diatoms founded on the mode of division of the chromatophores. 



* La Nuova Notarisia, xii. (1901) pp. 129-3G (1 pi.). 



t SB. k. Akad. Wise. Wien, cix. (1900) pp. 769-801 (6 pis.) 



