99 



The loss of the power to act as germ cells or gametes which 

 the vast majority of the constituent cells in a typical multicellular 

 organism usually suffer is undoubtedly one of the penalties 

 which they have to pay for their high degree of speciali- 

 zation. The germ cells themselves, on the other hand, always 

 remain in a more primitive, less specialized condition, and 

 may, in fact, be regarded as so many unicellular Protista 

 enclosed within the multicellular body. They resemble the 

 free-living Protozoa and Protophyta also in that they exhibit a 

 certain degree of independence and are in the majority of cases 

 actually set free from the parent body as unicellular individuals ; 



FIG. 46. Fticus vesiculosus ; Section through a female Conceptacle, X 50. 

 (From Vines' " Botany," after Thuret.) 



short-lived, it is true, unless they happen to meet one another 

 and conjugate, but nevertheless enjoying that liberty which is 

 only possible to independent organisms. 



All this is very beautifully illustrated in the case of the common 

 brown seaweed or bladder- wrack, Fucns vesicidosus (Fig. 45). 

 The entire plant consists of flattened branches, copiously 

 subdivided and attached by a root, usually to some rock between 

 tide-marks. Here and there the branches are swollen out to form 

 air-bladders (/>), which serve as organs of flotation. The 

 histological structure of the plant is comparatively simple and 

 need not detain us ; we are concerned only with its reproductive 

 processes. 



Fucus vesiculosus is dioecious or unisexual, there being distinct 



H 2 



