182 SUMMARY OF CUERENT RESEARCHES RELATING TO 



wliich consists mainlj of carotin, probably serves for the absorption of 

 heat, for protection against Hght, and for reserve material. The 

 carotin takes no part in assimilation. 



Hydrodictyon.* — S. Yamanouchi describes a new species of Hydro- 

 dictyon, H. africanum^ which appeared in a culture of soil sent from 

 Valkenberg- Ylei, near Cape Town. Its development from the early 

 stages was carefully watched, and is here figured and described. It 

 differs from H. reticidatum in size and habit, as well as fundamentally 

 in the structure of the cell, by possessing definite plastids in which 

 starch is formed. The division of the nucleus is described and figured. 

 Gametes (? zoospores) were observed. 



Sporulation in Diatoms.f — L. Mangin writes an account of the 

 sporulation of diatoms, giving the work and views of former authors 

 and the state of our knowledge at the present. Two kinds of spores 

 exist among diatoms : statospores or endocysts, and microspores. The 

 endocysts are protoplasmic masses condensed in the interior of the 

 valves of an individual, covered with a siliceous shell of two valves, 

 often ornamented. They have frequently been described as distinct 

 species, Dicladia, etc. When liberated they fall to the bottom of the 

 sea. They occur at the end of each period of vegetation. Among 

 plankton diatoms, two series may be distinguished. One is formed of 

 individuals capable of producing endocysts, which reproduce the species 

 after a resting period. The other comprises dimorphous species such as 

 Chsetoceros didymus, etc., which present first purely vegetative indivi- 

 duals, and later reproductive individuals destined to produce only 

 endocysts. Speaking generally, the author holds that endocysts 

 characterize neritic diatoms, and microspores pelagic diatoms. Certain 

 species, however, possess both formations. The formation of micro- 

 spores explains the sudden appearance of a species in masses. Mangin 

 insists on the unsatisfactory methods of collection, by which the smallest 

 organisms escape through the finest meshes ; also on the frequent 

 injury to the organisms, which prevents a series of observations of 

 development. 



False Conjugation of Diatoms. J — E. Penard describes some in- 

 stances of false conjugation of diatoms frequently observed in the Lake 

 of Geneva. The species concerned are Navicula viridis, Cymatopleura 

 solea, and C. elUptica. The arguments against its being a true conjuga- 

 tion are that cliains are unknown in these species ; that one individual 

 is generally smaller than the other ; that sometimes not two, but three 

 individuals become united at a common point. When two diatoms 

 meet, one 2:lides over the other till the little mucilas:inous mass in its 

 rear catches against that of the other diatom and cannot be detached. 

 The third one breaks away when an attempt is made to mount the 

 group. The nucleus shows no special change. The unions occur only 

 between members of the same species. 



* Bot. Gaz., Iv. (1913) pp. 74-9 (figs.). 



t Rev. Sci., 1912, pp. 481-7 (figs.). 



X Bull. Soc. Bot. Geneve, iv. (1912) pp. 245, 248-9. 



