HISTORY OF DIATOMS. 



23 



4. Lastly the Rev. Wm. Smith has described a fourth method of re- 

 production, in which a single frustule 

 gives birth to two sporanges. This 

 phenomenon has been recorded in 

 Achnanthes and Rhabdonema, but 

 as it has never been since observed 

 it is thought that it must have been 

 an error in observation on the part of 

 the illustrious English diatomist. 



To sum up it seems probable that 

 diatoms most frequently return to 

 the sporangial form by an act of 

 rejuvenescence without actual repro- 

 duction, but that when it really does 

 take place it is produced by the 

 union of two frustules, which give 

 birth sometimes to a single sporange, 

 but generally to two sporanges. 



We shall here draw attention to a 

 very remarkable idea ventilated by 

 Dr. Ad. Schmidt. "I observed," 

 said he, "in 187 1 the regeneration 

 of Gomphonema mustella Ehr in 

 thousands of cases, and what I have 

 just said has not been invalidated by 

 a single exception. When these 



Fig. 16. 



Fig. 16 Reproduction of I'an Heurckia rhom- 

 boides Brcb. 



A. Two mother cells fusing their protoplasmic 

 contents in order to form two sporanges. 



B. Two auxospores larger than the four 

 empty valves, between which they are formed, 

 arrived at their complete development and at the 

 point where the terminal hoods detach them- 

 selves to enable the sporangial frustules to pass. 



C. Sporangial frustules arrived at their com- 

 plete development and still covered with the Gomphonema reproduce they have 



hoods which they have drawn along on leaving ... . . .... 



the auxospores. their stipes, and unite with their 



venters turned towards each other, but in an inverted position, that is 

 to say, so that the anterior apex of one frustule rests against the 

 posterior apex of the other." " This fact," he concluded, " in my opinion 

 disposes of the vegetable nature of diatoms." (! ?) 



In concluding this section it may be noticed that, according to Kitton (') 

 and Professor Samuel Lockwood, ( 2 ) diatoms may possess microspores so 

 small that they can pass through filter papers. Lockwood appears to 



(') Kitton: On the Mysterious Appearance of a Diatom, J.Q.M.C, Ser. II., Vol. II. (1885), 

 pp. 178-9; 206. J.R.M.S (1885), p. 1,041. 



( - ) Lockwood, Prof. Samuel : Raising Diatoms in the Laboratory. Journal New York Mic. 

 Soc. (1886) II., p. 153, two plates; J.R.M.S. (1887), p. 626. 



