VIII] OR CELL-AGGREGATES 409 



only we clearly understood the actual conditions, is indicated in 

 the development of the antheridium 

 of a fern, as described by Strasbiirger. 

 Here the antheridium develops from 

 a single cell, whose form has grown 

 to be something more than a hemi- 

 sphere ; and the first partition, instead 

 of stretching transversely across the 

 cell, as we should expect it to do if 

 the cell were actually spherical, has 



as it were sagged down to come in Kg. 193. Development of anthe- 



contact with the base, and so to develop ridium of Pteris. (After 



. Strasbiirger.) 



into an annular partition, running 



round the lower margin of the cell. The phenomenon is akin to that 

 cutting off of the corner of a cubical cell by a spherical partition, 

 of which we have spoken on p. 349, and the annular film is very 

 easy to reproduce by means of a soap-bubble in the bottom of 

 a cylindrical dish or beaker. The next partition is a perichnal 

 one, concentric with the outer surface of the young antheridium ; 

 and this in turn is followed by a concave partition which cuts off 

 the apex of the original cell : but which becomes connected with 

 the second, or periclinal partition in precisely the same annular 

 fashion as the first partition did with the base of the little 

 antheridium. The result is that, at this stage, we have four 

 cell-cavities in the little antheridium: (1) a central cavity; 

 (2) an annular space around the lower margin ; (3) a narrow annular 

 or cylindrical space around the sides of the antheridium ; and 

 (4) a small terminal or apical cell. It is evident that the tendency, 

 in the next place, will be to subdivide the flattened external cells 

 by means of anticlinal partitions, and so to convert the whole 

 structure into a single layer of epidermal cells, surrounding a 

 central cell within which, in course of time, the antherozoids are 

 developed. 



The foregoing account deals only with a few elementary pheno- 

 mena, and may seem to fall far short of an attempt to deal in general 

 with "the forms of tissues." But it is the principle involved, 

 and not its ultimate and very complex results, that we can alone 



