OF CONFERVA. 



139 



sphere which eventually became a universe of attractions for the 

 whole circle of scientific minds. 



Thuret's task in the investigation of the mode of growth and 

 reproduction of the simplest branching water-weeds, was to show 

 what is the nature of the apparent increase in the complicity 

 of the progressively more elevated forms. The first and simplest 



step in this way is exhibited by a very common 



green sea- weed which is called Bryopsis (figs. 80, 81). 



Notwithstanding that it differs 



so much, to all appearances, 



from the snow-plant, and seems 



to be much more complicated c| 



than that, yet in reality it is 



scarcely more elevated in rank 



than the little globule whose de- 

 velopment we have just followed 



Fig. 80. through. It has made an initiatory step, however, 

 toward a higher status by a differentiation of its whole into 

 stem and top, and by assuming the form of the more highly or- 

 ganized aquatic plants ; although the organization is rendered 

 none the more complicated by the manner in which this is done. 

 This you will readily comprehend if I suppose, for instance, that 

 the globular cell of the snow-plant were so plastic that you could 

 stretch it out into a long tube, and then draw out the sides of the 

 tube into numerous parallel, finger-like projections (like fig. 80, 

 a) ; you would still have a single cell, with a single cavity 

 within it, and therefore in reality no more complicated than 

 before. Such is the condition of Bryopsis. The process of re- 

 production is the same as in the snow-plant ; the whole contents 

 become changed into lively, moving spores, (fig. 81, B, C,) each 

 furnished with from two to four vibrating cilia. The entire 



Fig. 80. Bryopsis plumosa. A young plant from our coast, a, the pinnules, 

 or lateral projections. Original. 



Fig. 81. Bryopsis hypnoides. a, the aperture of a pinnule like a of fig. 80; 

 B, C, zoospores, one with two, and the other with four vibratory cilia, magnified 

 330 diameters. From Thuret. 



