488 



LIFE-HISTORIES 



Fig. 317. — -Sea-tangle. Transverse section through the outer part of a 

 stalk 2 cm. in diameter, ^^, showing the darker rind (r, r) containing 

 slime-canals {g, g) ; and the lighter interior tissue (p, p) which form the 

 greater bulk. (Luerssen.) 



Fig. 318. — Bladder-wrack (Fucus vesicitlosus. Wrack Family, Fucacece). 

 Branch bearing air-bladders (/) and swollen tips (s) containing con- 

 ceptacles. (Luerssen.) — Brown, slimy, tough seaweed, sometimes 1 m. 

 long, growing attached to rocks, etc., between tides along the North 

 Atlantic coast. 



A comparatively simple type is the thread-weed (Xcmalion, 

 Fig. 320). The thallus is small and with slender brandies wliich 

 grow at the apex but do not show much differentiation among the 

 vegetative cells. Male gametangia (/, sp) are developed at the tips 



