192 



COMPENDIUM OF GENERAL BOTANY. 



A. FORMS OF REPRODUCTION AMONG 



Although the phenomena under discussion differ very greatly r 

 we are enabled to see (among algae) a well-marked relationship ; 

 there is, in general, an alternation of generation between sexual 

 and asexual methods. 



Among Desmidiaoece (unicellular algse) asexual reproduction 



by division alternates with reproduction by the conjugation of mo- 



tionless gametes (see Fig. 19 in regard to reproduction by division). 



Peculiar and interesting conditions are met with among the 



Diatomacew, 1 a group of unicellular yellowish-green algse en- 



closed by a silicious mem- 

 brane characterized by 

 very beautiful and deli- 

 cate striations and mark- 

 ings. A highly delicate 

 organization associated 

 with great reduction in 

 size characterizes these 

 truly marvellous creat- 



ures. (E H R E N B E R (>, 



1835. OTTO MULLER, 

 Berlin, is at present well known as a specialist on diatoms.) Space 

 will not permit a fuller discussion of the delicate structural markings ; 

 we can only mention them in so far as they are concerned with the 

 processesof reproduction. The two parts of the silicious shell of the 

 diatom fit each other as do the body and cover of a pasteboard box. 

 For a series of generations reproduction is the result of simple divi- 

 sion, hence asexual ; then follows a special sexual generation (conju- 

 gation), which is again followed by division, and so on (see Figs. 116 

 and LIT). 



The following statements are based upon direct observation. 

 (1) Every division of a cell forming a diatom-individual (after 

 cell-wall formation and separation of the two cells) gives rise to one 

 (A) daughter-cell, equal in size to the mother-cell, and one (B) 

 smaller daughter-cell. (2) There is no growth in length ; as a result 

 the smaller individuals must continually increase in number. The 



A 



FIG. 116. Diagramatic 

 tation of two diatoms, 

 view. 



B 



resenv 

 teral 



FIG. 117. Top 

 view of dia- 

 tom. 



(Berthold and 

 , Landois ) 



1 PFITZER made very important investigations of this group. 



