FUCUS VESICULOSUS. 305 



in the direction in which the beaks of the majority of the sperma- 

 tozoids are directed ; should the direction of rotation change, 

 it is due to the attachment of new spermatozoids, thus altering 

 the orientation of the majority. The movement is no doubt the 

 resultant of the component movements of the spermatozoids ; 

 but if the movement tends to maintain any uniform direction, 

 the spermatozoids arranged in any other direction tend gradually 

 to alter their position, and to assume one corresponding with the 

 movement. In addition to the attached spermatozoids, the oos- 

 phere appears to be surrounded by a swarm of free spermatozoids, 

 which move within its sphere of influence (Fig. Ill, H). In from 

 ten to twenty minutes the rotation ceases, and there is no doubt 

 that fertilisation has been effected, by the absorption of a sperma- 

 tozoid ; although, owing to the opacity of the oosphere, it cannot 

 be observed. The fertilised egg, or oospore, has likewise 

 developed an exceedingly delicate membrane. If a quantity of 

 oospheres are mingled, as above, with spermatozoids, either on 

 a hollow object-slide or watch-glass, and, after a few minutes, 

 fixjed and stained with iodine solution, we may be able to see 

 the results of fertilisation. In most of the oospheres two nuclei 

 can be seen : a larger one, with large nucleolus, the oo-nucleus ; 

 and a usually somewhat smaller one, with smaller nucleolus, 

 representing the spermo-nucleus, or nucleus of the absorbed 

 spermatozoid. The penetration of the spermo-nucleus towards 

 the centre of the oosphere must take place very rapidly, for we 

 find it commonly already in the neighbourhood of the oo-nucleus. 

 In some of the oospheres the two nuclei have already been 

 combined into a single one, in which process lies an essential 

 characteristic of fertilisation, The embryo-nucleus, the result 

 of the copulation of the oo-nucleus and spermo-nucleus, shows at 

 first two, but later on only one, nucleolus. 



Reproduction in Char a. The small family of the Characeae, 

 or Stoneworts, occupy a somewhat isolated position in the vege- 

 table kingdom, but are best placed amongst the green Algae. 

 Their structure, both vegetative and reproductive, is unique. 

 They have a jointed stem, at the nodes of which leaf -like whorls 

 of branches are borne. The internodes between two whorls are 

 unicellular (as is noted on p. 246), and are either bare, or covered 

 with a kind of cortical sheath of cells. The nodes are multi- 

 cellular disks, bearing the branches on their periphery ; from 

 the nodes also proceed the cells which form the cortical invest- 



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