26 SURVEY OF THE REPRODUCTIVE PROCESS 



may, of course, be extended to the whole frond. But in 

 the Desmidiese and Diatomaceae, in which the spore is formed 

 outside the cells, and in Mesocarpus among the Conjugatse, 

 in which it is lodged in a dilatation of the connecting pas- 

 sage, we can only in a general way allege indications of 

 sexuality, having no guide to determine which is male and 

 which female.* 



The modifications of conjugation just noticed may be 

 arranged as follows : — 



I. In isolated cells : 



1. Fusion of two pseudo-cells into one — Palmoglea.'f 



2. Dehiscence of two cells, and fusion of their contents 



into a single spore — Desmidiese. 



3. Effusion of the contents of two cells, and formation 



from thence of two new frustules, larger than 

 those in conjugation — Diatomaceae. 



II. In cells aggregated into filaments — Conjugatse. 



4. Contents of two cells in different filaments effused 



into a dilatation of the connecting tube, and 

 there formed into a spore — Mesocarpus. 



5. Contents of the cells of one filament passing pro- 



miscuously into those of others, through com- 

 municating tubes, the recipient cells maturing 

 the spores — Mougeottia. 



6. Conjugation of the same kind between adjoining 



cells of the same filament — Rhynchonema. 



7. Conjugation of the same kind, one filament evacu- 



ating the contents of aU its cells into those of 

 a connected filament — Spirogyra. 



* Carter remarks tLat in Spirogyra the recipient cell is generally tlie 

 larger of the two, and hence suggests that the inequality in the size of 

 the conjugating frustules which is occasionally observed in Diatomacese 

 may also possibly have a sexual import. Ann. Nat. Hist., 3d Ser., I. 35. 



f Braun, Rejuvenescence in Nature, pp. 136 and 327. 



