40 HALF AN HOUR WITH SEAWEEDS. 



which naturalists have found so difficult to reconcile 

 with vegetable life. The species of " sea-wrack/' how- 

 ever, that is best known, especially for the explosive 

 power of its bladders when treated in the manner 

 aforesaid, is the " knotted wrack " (Fucus nodosus, 



Fig . 9 . Kg- 9). In this 



species the recep- 

 tacles which form the 

 fructification are not 

 terminal, as in that 

 just mentioned, but 

 are borne in stalks or 

 pedicels issuing from 

 either side of the 

 fronds. In the " knot- 

 ted wrack," also, the 

 spore separates into 

 four, whence their 

 name of tetraspores 

 (Fig. 9 a). In the 

 " serrated wrack," 

 however, these spores 

 divide into eight 

 parts, called sporules. 

 Another kind of 

 wrack, nearly as well 

 Knotted Wrack (Fucus nodosus). kno^n as the above, is 

 the Fucus canaliculatus, having fronds only a few inches 

 in length, and the spores separated into two spores (see 

 Fig. 10 a). Besides the above, there are two or three 



