792 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Structure of Diatoms.* — According to L. Eeinhardt a form of 

 valve similar to that described by Miiller in Triceratium, occurs in 

 many, if not all forms with areolated cell-wall. 



The formation of the pedicel and of gelatinous colonies are 

 phenomena altogether analogous to those which occur in the palmel- 

 loid algae. In the Mastogloea colonies it is easy, when the formation 

 of jelly has not advanced beyond a certain extent, to observe a similar 

 system of intercalation of cell-walls as in Gloeocystis. In the cell-wall 

 of Mastogloea and other similar forms, two layers can be distinguished, 

 an outer gelatinous, and an inner layer which retains its consistency 

 and structure. In the formation of the pedicel the outer layer 

 becomes locally mucilaginous. In those forms where an entire group 

 of individuals is attached to a single pedicel (as many species of 

 Synedra and Licmophora) longitudinal striae make their appearance on 

 the thick pedicel corresponding to the separate cells ; these are made 

 distinctly visible by staining with hsematoxylin. 



The author also describes the formation of auxospores in Cocconeis 

 communis, Achnanihes longipes, and A. hrevipes ; in the first species 

 their development was followed out in several hundred specimens. 

 The auxospores are always formed by the conjugation of two in- 

 dividuals, never by rejuvenescence, as stated by Schmitz. The con- 

 jugating cells often open at different times, and the formation of the 

 mucilaginous bladders begins only with the coalescence of the con- 

 jugating masses of protoplasm. The nuclei of the conjugating cells 

 move slowly in the direction of the movement of the protoplasm 

 towards the anterior margin of the masses of protoplasm, and, a short 

 time after these commence to coalesce, a single much larger nucleus 

 is seen in the place of the two. Conjugation of the nuclei therefore 

 takes place here. The author further describes the formation of the 

 perizone and of the cell-wall of the auxospore, the growth and bipar- 

 tition of the chromatophores, and the division of the auxospores into 

 two primary cells. In Aclinanth.es longipes the conjugation always 

 takes place in a very interesting way between two cells which are not 

 equivalent. One of these has always a long pedicel, whilst the other 

 is attached by a gelatinous disk to the upper end of the pedicel of the 

 first. When the protoplasmic masses of two cells coalesce, a mucila- 

 ginous bladder is formed, which is connected only with the lower 

 valve of the stalked cell. Since this bladder is formed essentially 

 from the protoplasm of the stalked cell, it follows that that of the 

 other cell passes into the bladder of the first. The phenomena in 

 this species justify the regarding of the formation of auxospores by 

 conjugation as a process of sexual reproduction. In A. hrevipes the 

 process is the same in its general features. The formation of auxo- 

 spores without conjugation is regarded by the author as a kind of 

 apogamy. 



* SB. Vers. Euss. Naturf. u. Aerzte, Odessa, Aug. 27, 1883. See Bot. 

 Centralbl., xviii. (1884) p. 191. 



