372 



BOTANY 



covering, the spermatozoids appear as somewhat elongated, ovate bodies, having 

 two lateral cilia of unequal length and a red eye-spot. The oogonia (Figs. 307 o, 

 308) are nearly spherical, and are borne on a short stalk consisting of a single cell. 

 They are of a yellowish-brown colour, and enclose eight spherical egg-cells which 

 are formed by the division of the oogonium mother cell. The eggs are enclosed 

 within a thin membrane when ejected from the oogonium (Fig. 308 B, C). This 

 membranous envelope deliquesces at one end and, turning partly inside out, sets 

 free the eggs (D, E). The spermatozoids then gather round the eggs in such 



FIG. 309. Fucus. 1, Group of antheridiu. ..'. 1'ait of an antliri idimii sliouin- 



spermatozoid.s. "3, Spermatozokl : o, eye-spot ; k, nucleus. ^ Isolated 'antheridia liberating tbfl 

 spermatozoids. 5, Oospliere surrounded by spermatozoids. 6, Section through a 1'<>i tili.-''<l i-.^.n : 

 ek, nucleus of epp : >',/>/.. sperm-nucleus ; sp, s))ermatozoids. (1, If, f>, after THURET ; 2, :>, a ft IT 

 GCIGNARD ; 6, after FARMER. From OLTMANNS' Algae.) 



numbers that by the energy of their movements they often set them in rotation 

 (Fig. 309, 5). After an egg has been fertilised by the entrance of one of the 

 spermatozoids (Fig. 309, 6) it becomes invested with a cell-wall, attaches itself 

 to the substratum, and gives rise by division to a new plant. 



In the case of other Fucaceae which produce four, two, or even only one egg in 

 their oogonia, the nucleus of each oogonium, according to OLTMANXS, nevertheless 

 first divides into eight daughter nuclei, of which, however, only the proper 

 number give rise to eggs capable of undergoing fertilisation. 



Since the Fucaceae have no asexual spore- formation the alternation of genera- 

 tions characteristic of Dictyota is wanting in them. It is possible to regard the 



