THE SHORES OF BRITAIN. 3l 



narrow fronds, resembling leaves, divided iutc 

 branches, and having a midrib nmning through the 

 centre ; the leaf-like branches terminate in large 

 greenish or yellow oval receptacles, the former con- 

 taining many seeds, enveloped in a thick mucus, the 

 latter some curious organs known as antheridia, analo- 

 gous to the anthers of flowers.* But its chief pecu- 

 liarity is, that the substance of the frond swells at 

 irregvdar interv^als into oval air-cells, always arranged 

 in pairs, one on each side of the midrib. The Dutch 

 use this sort, and another called Black-wrack [F. eer- 

 ratus), to pack their lobsters ; the latter, however, is 

 preferred, on account of its containing less mucus, and 

 therefore being less liable to fermentation. 



Scarcely inferior in its alkaline properties to the 

 Sea- wrack is the Knotted-wrack {F. nodosus). The 

 fronds look like slender stems, swelling at intervals 



* Recent microscopical investigations of the Fucacece, or Wrack- 

 weeds, have brought to light some unexpected facts of very high 

 interest, particularly those which are connected with the reproduc- 

 tion of therfe plants. Like the higher tribes of vegetable life, they 

 lu-e found to develoi> male and female organs, the former of which, 

 called Zoospores, have the power of free, spontaneous, and, ap- 

 jiarently, voluntary motion, vibrating their long threads, and 

 swarming over the germ-cells, which they thus fertilise. 



"To observe the Zoospores in motion," remarks Professor 

 If.ifvey, "fresh specimens (of Fucus serratus) collected iu winter or 

 early spring, having orange-coloured receptacles, should be removed 

 from the water and left to dry partially. As the surface dries 

 there will exude from the pores of the receptacles large drops of a 

 thicK orange-coloured liquid, which on being placed under a micro- 

 Bcope and moistened with salt water, will be found to be composed 

 of innumerable antheridia, from which will issue troops of Zoo- 

 Bpores, which, at the moment of their liberation, commence those 

 Btrange animal motions which have so much puzzled philosophera 

 to reconcile with vegetable life." — (Phytol. Brit.) 



