246 POND LIFE. 



the latter in the pollen ; they usually exist in the same flower, but 

 sometimes in different flowers, or even on different plants, as in a 

 case of which I shall speak presently : and in order that seed may 

 be formed it is essential that the contents of the pollen grains 

 shall reach the ovule. The contents of the two cells mix and 

 form an embryo, which, during the next season, grows into a new 

 plant. I have alluded to this again because it is an example of 

 the method of reproduction, which is most common among 

 living bodies. 



I will now describe this process in a very interesting plant, 

 called Vallisiieria spiralis, which is much higher in the 

 scale of existence than those we have been considering. It 

 lives at the bottom of ponds, and consists of two kinds of plants 

 corresponding to the two cells which we saw in CEdogoniwn. 

 The one bears flowers which contain only ovules (the large 

 round cells) ; and the other, flowers producing only pollen (the 

 small, moving cells). Now, it is necessary that these pollen-grains 

 should reach the ovule, and this cannot take place under water, 

 partly because the flowers grow on different stalks, and partly 

 because water destroys the pollen. What happens is this : — 

 The ovule-bearing flower grows up in a very long, spiral stalk to 

 the top of the water, and then the flower opens out. The pollen- 

 bearing flower has no long stalk ; it adopts a simpler way of 

 reaching the surface of the water. The bud simply breaks off 

 and floats up to the surface, and is drifted about by the currents 

 or the winds, until by-and-by it comes into contact with the 

 fixed flower. Thus the contents of the two cells, similar to those 

 which I have described before, find the means of uniting with, 

 each other. The fixed flower now closes and is drawn down again 

 to the bottom by the contraction of its spiral stalk, and seeds are 

 formed in a vessel contained in it, and thus the plant is enabled to 

 reproduce itself. Vallisneria spiralis is one of the most curious 

 of our fresh-water plants, and as it succeeds very well in small 

 aquaria, any of you may have the opportunity of watching these 

 processes. 



With this I shall take leave of the vegetable kingdom, and 

 proceed to the animals. Let me ask you for one moment to look 

 back at the Amoeba described in the last lecture to recall the 



