THE FLOWER 235 



We can follow with still greater certainty the effect 

 of the pollen upon the ovule by means of experiment. 

 In the first place we know that if the stigma is not 

 pollinated the flower will fade without producing any 

 seed or fruit ; further, when pollen -tubes have been 

 made to act under the microscope upon ovules, removed 

 from the ovary, it has been found that the effects of 

 fertilisation were manifested only when a pollen-tube 

 came into contact with an ovule. Finally, the partici- 

 pation of the male element has been most conclusively 

 proved by experiments in artificial hybridisation. If 

 the pistil of a flower is pollinated from another flower, 

 differing from the first, say in the colouring of the petals, 

 it is possible in some cases to produce a plant with 

 variegated flowers, i.e. flowers which have both the colour 

 of the petals of the one in which the pistil was fertilised, 

 and the colour of the other the pollen of which was used. 

 Obviously the effect of the male cell has manifested 

 itself in the plant which resulted from the process of 

 fertilisation. 



In order to accomplish the requisite pollination, 

 plants are provided with a number of various adapta- 

 tions. Let us dwell on some of them. Here is a plant 

 (Pilea) rather insignificant in appearance, but grown 

 in hot-houses on account of the following curious pro- 

 perty : whenever the flowering plant, covered with 

 unsightly little flowers, is sprinkled with water, small 

 clouds of dust rise here and there from its surface as 

 if from minute explosions. This phenomenon is due 

 to the stamens of this plant (coiled inside the flower 

 and very hygroscopic) suddenly uncoiling like springs, 

 and shedding the pollen out of their broken pollen- 

 sacs. The pollen scattered in this way easily reaches 

 the stigma. Let us study another case, this time 

 a plant living in quite a different medium a water 

 plant. All lovers of indoor aquaria are familiar with 

 their most common inhabitant, Vallisneria. The 



