BOTANICAL SUBJECTS. 271 



As so many botanists have considered the ovule as the homo- 

 logue of the sporange, the placenta of phcEuogams would be the 

 homologue of the cellular cushion from which the sporangia 

 emerge,* and the placentation of Osmunda regalis and others 

 would be that of a midrib, the parenchymatous lamina having 

 disappeared. 



As to dehiscence or splitting of the ripe ovary to let out the 

 seed^ the two principal kinds are along the marginal suture, or 

 along that of the midrib. It is possible that sometimes one may 

 be mistaken for the other, for in the case of Ophrys apifera, if 

 instead of splitting along the margins it split along the midrib 

 between the two rows of ovular bunches, the dehiscence would 

 appear marginal. 



That splitting may occur in various directions is only too 

 evident. Asa Gray, at p. 117 of his " Structural Botany," says, 

 " The spine of Fouquiera is a portion of the lower side of the 

 petiole or midrib, indurated and persistent, the rest of the leaf 

 separating by splitting when it has served its office. "| 



Once admit that splitting of the capsule can take place along 

 the midrib, that is, in a longitudinal direction, and you, at the same 

 time, admit that sj^litting can take place in all directions diagonally 

 and transversely, and in all ways, for if dehiscence can occur along 

 the midrib, it can occur along its branches — the nerves and veins — 

 which may have any direction. Or, as in many cases, where the 

 fruit is fleshy, it \\-ill not occur at all, and the seeds are let out 

 either by birds or insects or animals eating the fleshy part, or bv 

 its decay. Of course, where the contained seed is only one, no 

 dehiscence is needed, as in the samara and aJtene. 



Therefore, dehiscence when it does occur, can do so along the 

 margin, the midrib, or along any sub-division thereof. This would 

 include the transverse dehiscence of the Portulaca, the valvular 

 of Jeffersoiiia, the poppy, and others. 



What I said of the ovary would of course apply to the dehis- 

 cence of the anther, which presents some curious ways of letting 

 out its pollen. 



* Also the homologue of the receptacle from which the akeues of the 

 stmwbeny emerge. 



f Described iu Plant(t Wright iance, ii., 63. 



