IN ANNUAL AND BIKNNIAL PLANTS. 83 



except in certain rather unusual instances, yet stems habitually pro- 

 duce roots, whenever circumstances favor it, namely, when they are 

 covered by the damp. and moist soil, or rest on its surface. Roots 

 accordingly may be distinguished into primary and secondary. 



141. The Primary Root is that which originates from the root end 

 of the embryo in germination, including also its branches. If this 

 continues as a main root, it commonly forms a tap-root. But very 

 often the main root, is soon lost in the branches. Sometimes a 

 cluster of roots is produced directly from the lower extremity of 

 the radicle, as in the Pumpkin, and Indian Corn (Fig. 130). In the 

 latter the second and the succeeding short joints of stem also send 

 out roots. These are early instances of 



142. Secondary Roots, i. e. roots emitted by other parts of the 

 ascending axis than the radicle. Most creeping plants produce 

 them at every joint ; and" most branches, when bent to the ground 

 and covered with earth, so as to afford the moisture and darkness 

 they require, will strike root. So, often, will separate pieces of 

 young stems, if due care be taken ; as when plants are propagated 

 by cuttings. Cryptogamous plants, growing from spores and hav- 

 ing no embryo stem or axis to commence with, are furnished with 

 secondary roots only. 



143. Viewed as to the duration of the plant, roots are distin- 

 guished into annual, biennial, and perennial. 



144. Annual Roots are those of a plant which springs from the 

 seed, flowers, and dies the same year or season. Such plants 

 always have fibrous roots, composed of numerous slender branches, 

 fibres, or rootlets, proceeding laterally from the main or tap-root ; 

 or else the whole root divides at once into such fibrous branches, as 

 in all annual Grasses (Fig. 130). These multiplied rootlets are 

 well adapted for absorption from the soil, but for that alone. The 

 food which the roots absorb, after being digested and elaborated in 

 the leaves, is all expended in the production of new leafy branches, 

 and at length of blossoms. The flowering process and the maturing 

 of the fruit exhaust the vegetable greatly (in a manner hereafter to 

 be explained), consuming all the nourishing material which it con- 

 tains, or storing it up in the fruit or seed for its offspring ; and the 

 exhausted plant perishes at the close of the season, or whenever it 

 has fully gone to seed. 



145. Biennial Roots are those of plants which do not blossom until 

 the second season, and which die when they have matured their 



