SPERM ATOPHYTES: ANGIOSPEKMS 373 
ture, necessary for the chemical changes about to be 
made. 
The first conspicuous change noted in the seed after the 
absorption of water is the softening of the contents, the 
solid and insoluble starch, if that be the form of the food 
storage, being converted by a process of digestion into 
soluble sugar, ready for transfer. The digestive substance 
is known as enzyme, and the most abundant enzyme in 
seeds is diastase, which has the power of transforming 
starch into a sugar. Accompanying these changes there is 
to be noted a marked evolution of heat, so that if a large 
mass of seeds is set to germinating, as in the process 
known as malting, the amount of heat generated may be 
very great. 
The first part of the embryo to protrude from the seed 
is the tip of the hypocotyl, thrust out by the rapid elonga- 
tion of the upper part of the hypocotyl (Fig. 143, B). This 
protruding and rapidly elongating tip, which is to develop 
the root, now rapidly elongates and is very sensitive to the 
influence of gravity, responding by developing any curva- 
ture necessary to reach the soil. Penetrating the soil, and 
beginning to put out lateral branches, it secures the grip 
necessary for the extrication of other regions of the em- 
bryo. 
After some anchorage has thus been obtained, the upper 
part of the hypocotyl again begins a period of rapid elonga- 
tion, which results in the development of a curvature known 
as the " hypocotyl arch " (Figs. 143, C, and 143, a). In 
the case of the germinating bean this arch is the first struc- 
ture to appear above ground, and its pull upon the seed 
is very apt to bring it to the surface. 
Finally, the arch, in its effort to straighten, pulls the 
cotyledons out of the seed-coats and with them the stem 
tip, the axis of the plant straightens up (Fig. 143, ), the 
seed-leaves and sometimes other leaves expand, and ger- 
mination is over ; for with roots in the soil, and green 
