54 
PLANT MORPHOLOGY. 
the plant in a moist chamber, it will be found in the 
course of one or two days that the marks between 1 
and 5 have become much farther apart, and that the 
growth in this region is about three times that between 
5 and 10. This experiment indicates that the growth 
of the root takes place at or near the apex, this region 
being known as the point of growth, or point of vege- 
tation. 
Upon examining the tip of a very young root by 
means of the microscope, it will be seen that the growing 
point is protected by a group of thin-walled paren- 
chyma cells, and these constitute the root cap. The 
root cap varies in length, being most apparent in 
the roots of aquatic plants, or plants producing aerial 
roots. 
Just above the root cap there is developed a narrow 
zone of delicate hairs, which are usually simple and 
filled with protoplasm. These are known as root hairs 
and their function is twofold : (1) They secrete an 
acid which renders the inorganic substances of the 
earth soluble, and (2) they absorb these dissolved sub- 
stances for the nourishment of the plant. 
When the germinating root persists, it is called the 
main, tap or primary root; when it divides into a num- 
ber of similar branches it is known as a multiple primary 
root, as in dahlia. Branches may arise in addition. 
There are some plants which complete their cycle of 
growth in one year, and such plants are spoken of as 
Annuals. Other plants produce only roots, stems and 
leaves the first year. The roots are large and fleshy 
and contain large quantities of nutritive matter, which 
is stored for the use of the plant the following year, 
when it produces fruit and thus completes its cycle of 
growth. Plants of this class are known as Biennials, 
and the roots as root-tubers or tuberous roots. Plants 
