266 The Sex and Generative Organs of Plants. 



But in the real leaves of the flower, the stamina, and the 

 pistil, peculiar alterations take place, which require the 

 appearance of new parts, of which there was not the least in- 

 dication before. These are the pollen, which has been com- 

 pared to human semen, and the ova. 



These two parts are to be looked upon as the most 

 important portions of the generative organs in plants, and 

 as their special male and female parts ; the manner of their 

 origin and of their mutual operation in order to produce off- 

 spring, has of late years been investigated with most satisfac- 

 tory results from the perfection of microscopic observations. 



To comprehend more distinctly the process of generation, 

 we must yet cast a glance over the different parts of the 

 leaf. We may assume that the original type of a com- 

 pletely developed green leaf consists of three parts, the 

 vagina, petiole, and lamina. The vagina, is the part by 

 which the leaf is attached to the stem or branch. It 

 embraces a part of the latter, and so far it is concave to- 

 wards the inside, convex towards the outside. At its upper 

 end, it terminates in the petiole, where all the vessels 

 run closer together, and form a round or half-round body. 

 From this point, the more ramified and finer vessels branch 

 out in different directions, and while they are bound to each 

 other by a few layers of cellular-tissue, they form the upper 

 skin-like broadened portion, of the surface of the leaf, the 

 lamina. This surface is, by means of its numerous openings, 

 especially intended for the inspiration and expiration of air 

 and vapours, and for increasing and preparing the nutritious 

 juices. If now the leaf, altered by the higher impulse of re- 

 production, takes on the nature of a flower leaf, its three or- 

 ganic parts have other functions bestowed on them. The 

 green leaf which is changed into a stamen looses commonly 

 its vagina ; its petiole becomes a filament ; its lamina is chang- 

 ed into the anthers. In this last part the most important al- 

 teration takes place ; the cellular tissue which lies between 



