112 BacillariesB 



Schiller ('09) has observed the formation of microspores in Ch&toc&ras 

 Lorenzianum, a species occurring in the plankton of the Adriatic. He found 

 two types of microspores, one in which the cells were quite round, and another 

 of more oval form, one end being more or less acute. These spores varied 

 from 2*7 5 ^ in diameter, and were provided with a wall of hardened 

 protoplasm. Neither cilia nor any active movement could be observed. The 

 differences between the two types are regarded by Schiller as sexual, but 

 there is no proof of this, nor was it found out what became of these spores. 

 Selk ('12) has also found microspores in Coscinodiscus biconicus in the 

 plankton of the Elbe. 



The formation of microspores just described was in each case in 

 a plankton-diatom, but it would appear that such spores are sometimes 

 formed in other diatoms. Kitton's suspicions concerned a small species of 

 Achnanthes. Lemmermann has observed the production of microspores in 

 Melosira varians, a species which is often most abundant at the weedy 

 margins of ponds and ditches. Hustedt ('11) has also described and figured 

 apparent microspores in Eunotia lunaris, a diatom which is never a true 

 plankton-constituent. 



It should be clearly understood that with the exception of Karsten's 

 observations on Corethron Valdivit?, the fate of these presumed 'microspores' 

 has not been traced. Karsten's small spores were apparently non-motile 

 gametes, and it is possible that those observed by Schiller were also passive 

 gametes. The ' microspores ' of diatoms require much further investigation 

 before any definite statements can be made with regard to their general 

 nature and purpose. 



The observations of Bergon, and of Peragallo, in which motile spores or zoospores are 

 recorded in several species of diatoms 1 , require considerable confirmation before they can 

 be accepted. It is only too well remembered how the presence of an internal parasite 

 caused that most acute observer, Archer, to describe zoospore-formation in the 

 Desmidiacese. 



Murray ('97) has described a method of reproduction in certain marine 

 plankton-diatoms by the formation of spores of the nature of gonidia. By 

 successive divisions of the original protoplast as many as eight or sixteen 

 rounded gonidia were observed in Coscinodiscus concinnus. Other aggregates 

 of small Coscinodiscus-cells indicated that these gonidia probably developed 



1 Bergon (iu Le Micror/raphe Preparateur, xiii, 1905) has described the development of 32 or 

 64 spores within the cells of Biddutyhia mobiliensis. He states that these spores are motile, being 

 furnished with two long cilia, and that his observations are confirmatory of Rabenhorst's discovery 

 in 1853 of the reproduction of diatoms by zoospores. After further investigations Bergon has 

 given fuller particulars of the development of the motile spores, but has not succeeded in tracing 

 their fate. Peragallo (in Proc. Stat. Biol. Soc. Sci. d'Arcachon, viii, 19045 (1906), p. 127) has 

 also described the transformation of a diatom-cell into a sporangium, from which zoospores 

 ultimately escaped. 



