52 



FERTILIZATION AND FRUIT-FORMATION IN CRYPTOGAMS. 



Here the bladder splits into two lamellse, and finally the inner lamella becomes inflated, 

 bursts and shrivels up, leaving the eight ooplasts free (see figs. 202 ^ and 202 ''). 



Whilst a certain proportion of the individual plants of Fucus vesiculosus develop 

 ooplasts in the cavities in their lobes, other individuals give rise to spermatozoids 



in similar cavities (see 

 fig. 203 1). The cells 

 lining the hollows de- 

 velop papillose protuber- 

 ances which grow longi- 

 tudinally, divide and 

 form a ramifying mass 

 of cells as is shown in 

 fig. 2031 Here and 

 there the extremities of 

 branches in this mass of 

 cells have a dark brown 

 colour, and their pioto- 

 plasmic contents are 

 broken up into a number 

 of minute portions (the 

 spermatozoids). These 

 vesicles become detached 

 and collect at the orifice 

 of the cavity. This hap- 

 pens especially at the 

 time when that zone of 

 tlie sea-shore where the 

 wrack grows is left dry, 

 and the Fucus plants are 

 lying flat upon the stones, 

 and look like brown and 

 faded leaves. At the 

 recurrence of high-tide, 

 when the wracks are 

 aeain .submerged, the 



Fig. 203. — Fucus vesiculosus. 



aya. 



> Lonsitudinnl section tlirougli a portion of a th<illus including a cavity full of 

 antlleiiilia. - Antlieridia extracted from a cavity of tlie kind. 3 Spermatozoids 

 escaping from tlie antheridia. * Spherical ooplast covered with spermatozoids. 

 1x60; 2x160; s, <x360. (After Thuret.) 



cells full of spermatozoids 

 burst, and the tiny spermatozoids formed from their protoplasmic contents swarm 

 out into the surrounding water. Each spermatozoid has a shai'p and a blunt end, 

 exhibits a so-called eye-spot, and is furnished with two long cilia b}' means of which 

 it swims about in the water (see fig. 203^). Analogy to similar processes which 

 take place in Mosses makes it seem probable that the ooplasts above described 

 as lying near the orifices of cavities in the thallus secrete some compounds oi- 

 other — presumably organic acids — which attract the spermatozoids swarming in 



