52 



FERTILIZATION AND FRUIT-FOEMATION IN CRYPTOGAJIS. 



&^. 



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. 203'). The cells 

 lininsf 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 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 loft dry, 

 and the Fueug plants are 

 lying flat upon the stones, 

 and look like brown and 

 fadetl leaves. At the 

 recurrence of high-tide, 

 when the wracks are 

 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^). 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 or 

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



Fig. 203. — Fiiciis ve^(ndoms. 



• LoDgitudinal section through a portion of a thallus including a cavity full of 

 antheridia. - Anthevidia extracted from a cavity of the kind, s Spermatozoids 

 escaping from the antheridia. < Spherical ooplast covered with spermatozoids. 

 1x50; »xieO; 8, <x860. (After Thuret.) 



