152 VEGETABLE PHYSIOLOGY. 



loped, but those of reproduction are imperfect, and their seeds are unfertile after 

 one or two generations. 



Connected with this interesting subject of fertilization is the history of 

 Cwlehogyne ilicifolia, an Australian Buphorbiaceous shrub, which cannot be omitted 

 here. Its flowers are dioecious, and for many years female individuals have been 

 cultivated in Enghsh Botanic Gardens, which, without the co-operation of stamens 

 (for there is not a single male plant in Europe), have produced seeds which have 

 germinated, and produced in their turn individuals perfectly resembling the mother 

 plant. Here the production of fertile seeds without the intervention of pollen is 

 incontestable. But we do not think that this exceptional phenomenon (which has, 

 however, been almost authentically paralleled by Hemp and Mercurialis, both 

 indigenous dioecious plants) will overturn the admitted doctrine of the fertilization 

 of the ovule by the poUeu ; and we find no difficulty in admitting that Nature has 

 given to the seeds of certain dioecious plants a power of multiplied reproduction, 

 which may extend to several generations, such as is proved to exist in the case of 

 Aphides. Besides, the force of the anomaly presented by Gaelebogyne cannot be esti- 

 mated at its true value until time shall have shown whether this power is limited or 

 indefinite. 



The period of fei-tilization is that at which the flower exhales its perfume and 

 appears in its full beauty ; the stamens and pistil then exhibit spontaneous motions, 

 which in some species are very remarkable. Thus, in the Berheris, the filaments of 

 the stamens are at first pressed between the two glands of each petal, which as 

 they spread force the filaments to spread also ; these soon free themselves under 

 the stimulus of the sun, aided by a slight evaporation which has contracted these 

 and the glands which retained them ; when they quickly resume their original bent 

 position and approach the pistil, on which the anthers shed their pollen. This 

 action, which is efi'ected by the solar rays, may be artificially induced, either by 

 gently irritating the filaments, or by shaking the fiower ; for the least shake or 

 slightest touch releases the stamen. The same irritability is observable in Parie- 

 taria and in Nettles, the filaments of which lie curved back within the calyx, but 

 instantly spring up, if lightly touched; when the anther, which was previously 

 pressed down at the bottom of the flower, is carried up, and sheds a little cloud of 

 pollen. Rue sheds its pollen with less force but with better aim ; it has four or five 

 petals and eight or ten stamens ; on most flowers there is one stamen which, instead 

 of spreading horizontally over one or between two petals, bends over the pistil, 

 against which the filament presses. If patiently watched, the anther will be found 

 to open and emit the pollen ; when the stamen, having fulfilled its function, falls 

 back, and another rises to take its place, and so on in succession till all the anthers 

 have in turn shed their pollen on the pistil. The elasticity of the anthers is not 

 always sufficient to discharge the pollen on the stigma. The conditions under 

 which the pollen is discharged are very various ; in many cases the flower is fertilized 

 before expansion ; in many others, the anthers are placed above the pistil, and the 

 pollen is brought directly into contact with the stigma ; but it frequently happens 

 that the position of the stamens is unfavourable to their pollen reaching the stigma, 



