INTKODUCTION TO CRYPTOQAMIC BOTANY. 231 



nate when treated with the spermatozoids of F. serratus ; on 

 the contrary, those of F. vesiculosus, a species especially prone 

 to run into varieties, germinated freely under the same cir- 

 cumstances. The impregnation then is clearly of a nature 

 altogether similar to what obtains in those reptiles whose 

 eggs are fertilised, when free, by means of spermatozoa diffused 

 in the surrounding water.* 



219. A large portion of the Fucacew are supported in the 

 water by means of bladders formed in their stems or fronds, 

 such as have already appeared in Macrocystis, or in special pro- 

 cesses, often symmetrically disposed, and giving great beauty 

 to the species, in combiaation with the variously fonned recep- 

 tacles. The bladders are sometimes solitary ; but sometimes, 

 as in Halidrys, they form pods, containing a double row of 

 chambers. Besides these appendages, the fronds are often 

 sprinkled with little pores, producing a tuft of colourless fila- 

 ments proceeding from within. These probably act like the 

 delicate hairs on the roots of many Pha3nogams, exposing a 

 large surface to the surrounding medium capable of imbibing 

 nutriment, or effecting an interchange between the gases 

 which may exist in the plant and those which may be con- 

 tained in the water. The pores seem to be analogous to 

 stomates. 



220. Fucacece afford a large portion of the kelp and iodine 

 of commerce, and food to cattle. Like the Laminarice, they 

 supply an abundance of excellent manure. One or two genera 

 also, as D'UrvillcEa and Sarcophycus, are useful in other 

 respects to men. 



221. The numerous generaf in this tribe are distinguished 



* Capt. Carmichael was, 1 believe, tlie first to ascertain the double 

 system of organs in Fucaoecs about thirty-five years ago ; but, like many 

 of his discoveries, for want of a proper medium of publication during 

 his life, and especially owing to the disastrous state of the book-trade 

 a short time previous to his decease, this also remained in manuscript. 



t Decaisne and Thuret have proposed genera for our common 

 FxicacecE, depending on the number of the spores and other points con- 

 nected with the fruit. Thus Fucus nodosus=Ozothallia, Fucus canali- 

 culatus=Pelvetia. 



