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PHENOMENA OF REPRODUCTION. 



Fertilization. Under Organography, the fertilizing action of the pollen on the 

 ovules was alluded to, but not explained ; we shall now analyse some details of 

 this wonderful process, the most important of all departments of Vegetable 

 Physiology. ., f 



The ancients had confused ideas as to the nature of the stamens ; the botanists 

 who wrote after the Renaissance hazarded some vague conjectures on this subject ; 

 and it was only towards the end of the seventeenth century that their true functions 

 were assigned with precision to the pistil and stamen. Tournefort rejected the fact 

 of fertilization, and persisted in considering the stamens as organs of excretion. 

 After his death, the most devoted of his disciples, Sebastian Vaillant, in a discourse 

 delivered in 1716 at the King's garden, explained the functions of the stamens, and 

 demonstrated incontrovertibly the phenomena of fertilization in plants. Thanks 

 to this discovery, the date of which is known, France claims the honour of the 

 most important discovery which had hitherto been made in Botany. Eight years 

 later, Linnseus popularized the doctrine of fertilization by his writings, which were 

 no less remarkable for their learning than for their logical accuracy and poetic 

 charm. 



A few examples will suffice to prove the necessity of the pollen to fertilize the 

 ovule. The Date is a dioecious tree, whose fruit is the principal food of certain 

 eastern nations. From time immemorial these have habitually suspended panicles 

 of male flowers on the female plants, when fertilization invariably ensues. These 

 nations, when at war, destroy their enemies' male Date-trees, and so starve their 

 owners by rendering the female plants sterile. 



When the rainfall is excessive at the flowering season of the Vine, the growers 

 say that the vine runs, i.e. that the pistils are abortive ; whicli is owing to the pollen 

 having been washed away, and fertilization having consequently not been effected. 

 In newly-discovered Pacific islands, dioecious Cucurbitacece introduced for the first 

 time have produced female flowers ; but there being no males, fertilization has 

 never taken place. Botanists can prevent or produce fertilization by cutting away 

 all or some only of the stigmas of a pistil ; in the latter case the ovaries corre- 

 sponding to these stigmas do not produce seed. A pistilliferous Palm cultivated in 

 a hothouse at Berlin had been sterile for eighty years, when some pollen from a 

 staminiferous plant of the same species was sent by post from Carslruhe, by whicli 

 the Berlin tree was fertilized; it was then left sterile for eighteen years, after which 

 time it was again artificially fertilized, and the operation succeeded as at first. 



Experimenters have employed other means to demonstrate the physiological 

 action of the stamen ; they have placed the pollen of one species on the stigma of 

 a different species, belonging to the same genus, when individuals have been 

 produced partaking of the nature of both species. Plants thus produced by cross 

 fertilization are termed hybrids ; their organs of vegetation are pretty well deve- 



