386 



BOTANY OF THE LIVING PLANT 



its large size giving such security of germination as to justify the reduction 

 in number to one. 



In Fucoids which live submerged the gametes may be set free at 

 any time. But when exposed between tide-marks it will be chiefly 

 on the rising tide that they are liberated. Exposed to the air the 

 mucous thallus shrinks on drying, and the pressure of the contracting 

 tissue may be seen to squeeze out the ripe antheridia and oogonia, 



FIG. 326. 



I.-IV. Drawings direct from successively older Plants of Fucus serratus, showing 

 the regular dichotomy. 



which may be recognised by their yellow or olive colour, through the 

 open pores of the conceptacles. If these be collected fresh in separate 

 watch-glasses in sea water, the final liberation of the minute motile 

 spermatozoids (Fig. 324, 4) and of the much larger non-motile eggs 

 (Fig. 325, E) can be easily followed. If then a drop of water containing 

 the former be added to a drop containing ova on a slide, many sperma- 

 tozoids will be seen to collect round each ovum, which thus shows 

 its attractive influence on their movements (Fig. 324, 5). But only 

 one penetrates each egg, and its nucleus has been followed on its 

 course through the cytoplasm till it fuses with the nucleus of the 





