4 THE PLANT. 



dark, dry, and warm, where tlie atmosphere was seldom 

 changed — was fomid to have produced, from each bud, 

 a simple white shoot many feet long, showing no traces 

 of leaves, but covered with hundreds of minute potatoes, 

 which exhibited the same internal structure as tubers 

 grown in a field ; the cells consisted of cellulose, and 

 were filled with minute starch granules. It is certain 

 that the starch of the mother tuber, to have moved away 

 from its position, must have become soluble ; but it is 

 equally clear that in the developement of the shoots a 

 cause was operative within them, which (in the absence 

 of all outward causes whereon growth depends) recon- 

 verted the dissolved constituents of the mother tuber 

 into cellulose and starch granules. 



The conditions required for the germination of a seed 

 are — moisture, a certain degree of heat, and access of 

 air ; where one of these conditions is excluded, the seed 

 will not germinate. By the influence of the moisture 

 which the seed absorbs, and which causes it to swell, a 

 chemical action takes place in it ; one of the nitrogenous 

 constituents acts upon the others, and upon the amylum, 

 so that by a transposition of the elementary particles, 

 the constituents are rendered soluble ; the gluten is 

 converted into vegetable albumen ; the amylum and oil 

 into sugar. If the oxygen of the air is excluded, the 

 changes either do not take place or they proceed in a 

 different way. The seeds of land-plants, when submersed 

 under water, or placed in a soil covered with stagnant 

 water, which excludes the air, will not put forth their 

 plumules. This is the cause why many seeds, lying deep 

 in the ground or in bogs, will remain for many years 

 without germinating, although the conditions of moisture 

 and temperature be favourable. It is often found that 

 earth taken up from bogs, or brought up by the plough 



