SECT. I 



CRYPTOGAMS 



373 



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

 are formed by the division of the oogonium mother cell and are separated by 

 delicate cell walls. The eggs are enclosed within a thin membrane when ejected 

 from the oogonium (Fig. 298, B, G). This membranous envelope deliquesces at 

 one end and, turning partly inside out, sets free the eggs (Z), E). ■ The spermato- 

 zoids then gather round the eggs in such numbers that by the energy of their 

 movements they often set them in rotation (Fig. 299, 5). After an egg has been 



.« k 



Fig. 200. — Fncus. 1, Group of antlieridia. 3, Part of an antheridium showing developing 

 spermatozoid.s. S, Spermatozoid : o, eye-spot ; Ic, nucleus. A, Isolated antlieridia liberating 

 the spermatozoids. 5, Oosphere surrounded by spermatozoid s. 6, Section through a fertilised 

 egg: ek, nucleus of egg; spk, sperm-nucleus; sp, spermatozoids. (Z, /,, 5, after Thuret ; S, 

 3, after GuiQNARD ; 6, after Farmer. From Oltmanns' Algae.) 



fertilised by the entrance of one of the spermatozoids (Fig. 299, 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 Oltmanns, nevertheless 

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

 number give rise to eggs capable of undergoing fertilisation. The other reduced 

 eggs, incapable of fertilisation, degenerate. 



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

 tions characteristic of Dictyota is wanting in them. The thallus of Fhcus, 

 developed from the fertilised ovum, has diploid nuclei. Reduction takes place in 

 the first two divisions within the oogonium and antheridium, so that four haploid 



2b 1 



