200 



STRUCTURAL BOTANY 



\ 



cell-walls follow, and soon the oospore (which here does 

 not pass through a res ting-stage) is converted into a little 

 mass of tissue, but without at first changing its external 

 form. After eight or ten days, several root-hairs begin 

 to grow out at the end away from the light (see Fig. 

 86, B). They burst through the oogonial wall, which 

 has lasted all this time, and attach the embryo to the 



_^- -^ rock or whatever 



else it may be lying 

 upon. The upper 

 part of the embryo 

 now elongates and 

 becomes first 



1 -S $ : ''- * \ 



cylindrical and 

 then flattened at 

 the free end ; a 

 depression soon 

 arises at its apex, 

 in which a definite 

 FIG. 87. Ovum of one of the Fucacea! (^sco- apical cell appears, 



phyllum nodosum), seen in section at the g^cl now W6 have 



moment of fertilisation. <$, small male . ,, . , 



nucleus of a spermatozoid, which has traversed m a ^ essentials a 



the protoplasm, and is now in contact with new Pelvetia plant 



the large nucleus of the ovum. The proto- . -, -, 



plasm of the ovum shows a distinct foam-like I&lTiy 



structure. Magnified about 650. (After ^@ world. 

 Farmer.) 



In these Algae 



the result of fertilisation is a plant just like the parent. 

 There is no kind of asexual reproduction, and therefore 

 no possibility of any alternation of generations. 



We see, then, that in the order Fucaceae we 

 have the simplest possible life - history combined with 

 a very perfect form of sexual reproduction. The 

 plants are altogether very highly organised, as shown 



