FERTILISATION AND GERMINATION OF ZYGOTE 225 



cavity. They are expelled from the conceptacle at 

 low tide when the plants are exposed to the air, and 

 lie in masses in the film of water adhering to the slimy 

 surface of the frond. The masses of sperm bladders, 

 where these are separate from the eggs, can be easily 

 distinguished with the naked eye by their bright 

 orange colour due to the orange phseoplasts of the 

 sperms. The bladders enclosing the spermsi and eggs 

 then burst (Figs. 34, B, 35, C), setting the gametes free 

 in the film of water. 



The spherical egg contains much food material and 

 is many times the diameter of the sperm. It secretes 

 a substance of unknown nature which attracts the 

 sperms, and these, usually in considerable numbers, 

 cluster round it (Fig. 35, D), and by their constant 

 oscillation frequently set up a vortex in which the egg 

 rotates. One of the sperms eventually penetrates 

 the egg and the sperm nucleus travels across the 

 cytoplasm and fuses with the egg nucleus (Fig. 35, E, 

 F, G). Though the sperm nucleus is much smaller than 

 that of the egg, the amount of chromatin it contains is 

 seen to be equivalent in bulk, as is always the case. 



Development o£ the Young Plant. — ^The fertilised 

 egg (zygote) germinates at once. A cell wall is 

 secreted, the zygote lengthens, one end becoming 

 pointed, and the nucleus divides by a cross wall ; the 

 cell corresponding with the pointed end forming the 

 first attaching organ or rhizoid,^ which sticks to any 

 solid substratum with the help "of its mucilaginous 

 wall. The upper cell divides repeatedly, and this part 

 of the plant body elongates into a club-shaped form 

 (Fig. 33, B), fresh rhizoids meanwhile growing out at 

 the base. Very soon an apical cell is estabHshed on 



- Root-like organ, Greek pl^a, root. 

 15 



