VOL. XLVII.] PHILOSOPHICAL TRANSACTIONS. 179 



nettles, box, elm, birch, oak, walnut, beech, hazel, hornbeam, the plane tree, 

 pine, fir, cypress, cedar, the larch tree, melons, cucumbers, gourds, and several 

 others. In many of these, though the male and female flowers are at consider- 

 able distances, the farina foecundans, which Providence, on account of its being 

 liable to be spoiled by rain, or dissipated by winds, has provided in great abun- 

 dance, is conveyed to the female by means of the atmosphere. It is this class 

 of vegetables, and the following, the quantity of the produce of which is much 

 more precarious than those plants which have hermaphrodite flowers ; as the im- 

 pregnation of these last may be performed within their own calyx; whereas the 

 fonner must necessarily commit their farina to the circumambient air. It is for 

 this reason that if, during the time of the flowering of these plants, the weather 

 is either very wet or stormy, their produce of fruit is very inconsiderable, from 

 the spoiling or hasty dissipation of the male farina. Thus, independent of frosts, 

 the fniit of the nut and filberd tree is most numerous in those years, in which 

 the months of January and February are the least stormy and wet, as at that time 

 their flowers are produced. For the same reasons, a stormy or wet May destroys 

 the chesnuts; and the same weather in July prodigiously lessens the crop of mayz 

 or Indian corn, as its spikes of male flowers stand lofty, and at a considerable 

 distance from the female. In like manner a judgment may be formed of the 

 rest of these. Some of the more skilful modern gardeners put in practice, with 

 regard to melons and cucumbers, the very method mentioned by Theophrastus 

 200O years ago, in regard to the palm tree. As these plants, early in the sea- 

 son, are in this climate confined to frames and glasses, the air, in which they 

 grow, is more stagnant than the open air, by which the distribution of the farina 

 foecundans, so necessary towards the production of the fruit for the propagation 

 of the species, is much hindered ; to obviate which, they collect the male flowers 

 when fully blown, and presenting them to the female ones, by a stroke of the 

 finger they scatter the farina foecundans in them, which prevents the falling of 

 the fruit immaturely. 



Besides the vegetables before-mentioned, which bear male and female flowers 

 on the same root, there are others, which produce these oigans on different 

 roots: in the number of these are the palm-tree, (the more particular subject of 

 this paper,) hops, the willow-tree, misletoe, spinach, hemp, poplar, French 

 and dog's mercury, the yew-tree, juniper, and several others. Among these, 

 the valisneria of Linneus, as to the manner in which its male flower impregnates 

 the female, is one of the most singular prodigies in nature. The manner of this 

 operation is figured by Micheli, in his Nova Plantarum Genera, and described by 

 Linneus, in the Hortus Clifibrtianus. As that elaborate and expensive work is 

 in very few hands, Mr. W. here gives a short account of it. 



The valisneria grows in rivulets, ditches, and ponds, in many parts of Europe. 



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