144 WATER. 



ment in twenty-four hours; during this time carbonic acid is 

 given off. These phenomena plainly indicate the cause of the 

 heat during the period of fertilization. An inquiry of interest 

 suggests itself from these facts as to the changes efl^cted on the 

 flower by these operations. The disk and petals are now sup- 

 posed to act an important part in the process of fertilization, and 

 that the process of fertilization is the same as that of germina- 

 tion. The following conclusion confirms this hypothesis. In 

 both cases oxygen is absorbed, and an equal quantity of carbonic 

 acid given off. In both cases amylaceous substances disappear, 

 and a saccharine substance is generated. Heat also is alike 

 generated in both cases. The constitutions of the disk and 

 petals have been found to be similar to the nourishing p.-rts of 

 the seed. From these facts it has been concluded that the most 

 important function of the disk and petals is to afford nourish- 

 ment to the pollen and ovule, and the greatest vigor of these 

 organs is exhibited during the process of fertilization. After thia 

 effect has been accomplished, these organs wither. The honey 

 which is found in such abundance in flowers is the excess of the 

 saccharine production over what was required for the perfection 

 of the pollen, and the nourishment of the ovule. This excess 

 serves for the support of numerous insects, and yields the store 

 laid up by the Bee, which is gathered without injury to the plant. 



Section 3. — Water. 



276t We have already had occasion to remark on the im- 

 portance of water in vegetation, it being the only vehicle by 

 which the plant receives its nourishment, and by its decomposi- 

 tion and solidification constituting a considerable part of vege- 

 table products. It only remains for us to notice a few other 

 points connected with the operations of this agent. This ele- 

 ment, as it exists in the earth, holds m solution various earths 

 and alkalies, and vegetable and animal substances, and on this 

 account determines in a great measure the habitat of particular 

 families of plants. Those waters which contain much vegetable 

 substance nourish those vegetables whose tissues abound in 

 carbon, as our forest trees. The cruciferous plants, into whose 

 composition nitrogen enters as an element, seek localities in 

 which the waters may be more or less imjwegnated with animtd 

 substances. Some families of monocotyledons, which contain 

 more or less of silex, flourish best in those situations where the 



"What supposed action of the floral agents? What substance is generar 

 ted ? — 276. What office does water perform i i vegetation ? 



