8 FIRST GROUP. THALLOPHYTES. 



entrance into the oogonium has not yet been observed. The result of fertilisation is 

 that the contents of the oogonium clothe themselves with a cell-wall of their own, the 

 oospore thus formed increases considerably in size, and the formation of the cortical 

 layer (r) of the oogonium commences by the upward growth of branches from the sup- 

 porting cell (A, og"} ; these branches cling closely to the oogonium, and send out 

 branches of their own which also attach themselves closely to the oogonium and divide 

 transversely ; twigs also from other branches join in the formation (/?). All this takes 

 place in the period from May to July : while the contents of the rest of the cells of the 

 plant eventually disappear, the rind of the fructification assumes a dark brown colour. 

 The further development of the fructification begins in the ensuing spring ; a parenchy- 

 matous tissue is formed in it by repeated bipartition of its contents; the cortical layer 



FIG. 24. A part of a fertile thallus of Coleochaete pulmnata (magnified 350 times). B ripe oogonium in its rind. C germinating 

 fructifications of C. pttlvinata, in the cells of which the swarm-spores are formed. D swarm-spores (/>' D magn. 280 times). After 

 Pringsheim, 



bursts and is cast off (Fig. 24, C), and from each cell of the fruit proceeds an ordinary 

 swarm-cell, which in its turn gives rise to an asexual plant. In C. scutata, which shows 

 most variation from this course of development, the oogonia which are becoming invested 

 with their cortical layer lie in the plane of the disk, and the antheridia are formed by 

 division of cells of the disk into four. 



Pringsheim has drawn attention to various points of affinity between the Coleo- 

 chaeteae, Florideae, and Characeae, in his essay quoted above. 



The Conjugatae and the Characeae must now be examined in connection with the 

 Confervoideae. 



CONJUGATAE. 



The Conjugatae * consist of cells of limited growth, which multiply repeatedly and 

 to an unlimited extent by bipartition ; the cells thus formed live isolated or remain 

 united in rows. The chlorophyll in these plants has a striking appearance, the 

 corpuscles being disposed in parietal bands, in axile plates, or in pairs of stellate bodies. 

 Conjugation takes place between ordinary vegetative cells, the contents of which 

 coalesce in various ways. The body thus formed invests itself with a new cell-wall and 



1 De Bary, Unters. iiber die Fam. d. Conjugaten, Leipzig, 1858. 



