STRUCTURE.] THEORY OF THE PISTIL. 369 



of Tupistra, in which the apparent stigma is a fungous mass 

 with a surface of the same nature as mat of the style ; in 

 such a stigma the mode of fertilisation forms an interesting 

 problem,, which botanists have yet to solve. 



The centre of a stigma consists of tissue of a peculiar 

 character, which communicates directly with the placenta, 

 and which is called the conducting tissue. It is more lax 

 than that which surrounds it, and serves for the conveyance 

 of the fertilising matter of the pollen into the ovules. Schlei- 

 den says, that, as a style is a portion of a leaf rolled up, or 

 formed by a union of the edges of many leaves (as will be 

 presently shown), the centre of the style must answer to the 

 epidermis of the upper side of such leaf, and therefore this 

 epidermis, modified, constitutes the conducting tissue. If the 

 convolution or approximation of the carpels is very complete, 

 the tissue will be a mere thread ; but if it be imperfect, as in 

 Orchids, &c., the tissue will form the lining of a funnel- 

 shaped passage from the stigma to the cavity of the ovary. 

 But if, as I hope to have proved by the succeeding observa- 

 tions, the conducting tissue and the true stigmatic surface 

 are really an extension of the placenta itself, then Schleiden's 

 hypothesis requires to be modified or wholly abandoned. 



11*. Theoretical Structure of the Pistil. 



The foregoing is the common practical view that is taken 

 of the more remarkable peculiarities in the female system of 

 plants. This part, however, fills so important an office in 

 the functions of vegetation, is so valuable as a means of 

 scientific arrangement, and is liable to such a great variety 

 of modifications, that it is also necessary to regard it in 

 another and more philosophical point of view. For we have 

 yet to consider the structure of the compound pistil; to 

 understand the exact nature of its cells, and dissepiments, 

 and placentae, and the precise relation that these parts bear to 

 each other ; and also to prove that the necessary consequence 

 of the laws under which pistils are constructed is, that they 

 can be subject to only a particular kind of modification, 



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