224 SEXUAL REPRODUCTION (VAUCHERIA) 



diverse, but the adjacent sexual organs usually mature almost 

 simultaneously, so that self-fertilisation is probably the rule. 

 The more or less oval oogonium ($) develops a protrusion on 

 one side, whose tip becomes mucilaginous, and breaks down to 

 form the aperture through which the male cell enters. The 

 contents are rich in chloroplasts and at first multinucleate, but 

 in the mature egg, which possesses 'a pronounced receptive spot 

 opposite the opening, only one large nucleus persists. 



The antheridium is a coiled tube tapering slightly near the 

 apex, and giving rise, by division of its contents, to numerous 

 minute spermatozoids (Fig. 120, E, 3) ; the latter are pear- 

 shaped bodies with two laterally attached cilia, a very small 

 yellowish chloroplast, and a prominent nucleus (Fig. 120, G), 

 and are liberated by a breaking open of the tip of the antheridium 

 (Fig. 120, F). The attraction of the spermatozoid towards the 

 egg is probably again connected with the extrusion of mucilaginous 

 matter by the latter. After fusion, the oospore becomes en- 

 veloped by a thick wall and accumulates large stores of reserve 

 oil (Fig. 120, F) ; it then enters on the usual resting period, 

 which is ultimately terminated by the direct development of a 

 new plant. 



Apart from the vegetative propagation above described, 

 Fucus exhibits only sexual reproduction, the antheridia and 

 oogonia being developed in the large fertile conceptades occupying 

 the swollen tips of the thallus (Fig. 108, /). In some species 

 (e.g. F. platycarpus) the two kinds of sexual organs occur in the 

 same conceptacle, but in F. vesiculosus and F. serratus there are 

 distinct male and female plants. The globular cavities of the 

 conceptacles (Fig. 121, A) are separated from the rest of the 

 thallus by a wall (w.) composed of several layers of flattened 

 cells, from whose inner surface arise numerous unbranched 

 multicellular hairs which bend towards, and indeed often protrude 

 from, the small aperture ; in the fertile conceptacles the sexual 

 organs are interspersed among these hairs (Fig. 121, A). 



The oval oogonia possess a thick transparent several-layered 

 membrane, and are seated on a short stalk which arises directly 

 from the wall of the conceptacle (Fig. 120, H ; 121, A). At 

 maturity the contents are divided into eight uninucleate eggs, 

 containing abundant chloroplasts and separated by delicate 



