52 



FERTILIZATION AND FRUIT-FORMATION IN CRYPTOGAMS. 



Here the bladder splits into two lamellae, 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. 2031). Tjjg j,gjjg 



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 2032. Here and 

 there the extremities of 

 branches in this mass of 

 cells have a dark brown 

 colour, and their proto- 

 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 

 the 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 



Fig. 20s.— Fucus vesimlosns. j? i • i i • n 



recurrence of high-tide, 



1 Longitudinal section tlirougli a portion of a tliallus including a cavity full of i , 



antheridia. 2 Antlieridia extracted from a cavity of the kind, s Spermatozoids When the Wracks are 

 escaping from tlie antlieridia * Spherical ooplast covered with spermatozoids • i i . 1 



ix60;»xi60;»,''x360. (After Thuret.) again Submerged, the 



cells full of spermatozoids 

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

 out into the surrounding water. Each spermatozoid has a sharp and a blunt end, 

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

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

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

 as lymg near the orifices of cavities in the thallus secrete some compounds or 

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



