282 FUCUS. 



Examine in the same way the green slime from a female 

 plant, and note that it contains numerous oogonia, each 

 oogonium containing eight oospheres ; the firm extine 

 and mucilaginous intine of the oogonium are easily distin- 

 guished, and frequently at one end the stalk-cell remains 

 attached to the oogonium. In the dehiscence of the oogo- 

 nium, the extine bursts at the apex and the intine 

 protrudes ; the extine shrinks backwards, exposing more 

 of the intine which then swells and disappears, while the 

 oospheres, which have meanwhile become rounded off (in 

 the intact oogonium they are pressed against each other 

 and therefore polygonal), are set free as naked spherical 

 masses of protoplasm, containing chromatophores and a 

 central nucleus. 



Interesting permanent preparations of the developing sexual 

 organs, showing the numerous nuclei in the maturing antheridium 

 (which when young has a single nucleus) and the eight nuclei in the 

 maturing oogonium (which also begins with a single nucleus), may 

 be made as follows. Cut a fertile branch into pieces, each including 

 only a few conceptacles, and stain them in bulk by placing them in 

 borax carmine for 24 hours ; then place them in acid alcohol (2 drops 

 strong hydrochloric in 50 c.c. of 70 per cent, alcohol) until they be- 

 come clear red ; then place them successively in 70 per cent, alcohol 

 and in absolute alcohol about an hour in each ; then mount them 

 in a drop of clove oil on a slide, tease out with needles the contents 

 of the conceptacles sufficiently to show (1) the branching shrub- 

 like hairs bearing the antheridia, (2) the oogonia with the adjacent 

 paraphyses and lining tissue and mount in balsam. 



407. Fertilisation. Mix some orange slime and some 

 green slime in sea- water in watch-glasses. Also place a 

 drop of each on a slide and note that the antherozoids 

 approach the motionless oosphere and swarm around it, 

 giving it a rotating movement if present in large numbers. 



On keeping the mixed fluids in sea-water, note in a few 

 days that the oospore, which acquires a cell-wall after 

 fertilisation has occurred, becomes pear-shaped and divides 

 by a transverse wall, the fixed lower cell forming the hold- 

 fast while the upper produces the rest of the thallus. 



Young Fucus plants of different ages may also be seen 

 on rocks and stones, forming velvety olive-brown patches, 



