STUDIES IN VEGETABLE PHYSIOLOGY. 



STUDIES IN VEGETABLE PHYSIOLOGY— THE ROOT. 



BY AUGUSTUS FAHNESTCCK, SYRACUSE, N. Y. 



The third class of plants whose roots are perennial, or live an indefinite number of years, 

 is the largest of the three grand divisions. It comprises all our forest and shade trees, 

 and most of our beautiful flowering plants, and their forms are no less desirable than in 

 the foregoing grand divisions. The most common form of the perennial root is the branch- 

 ing. The roots resemble the branches of a tree, but have no regularity. Some of these 

 branches penetrate the earth to a great depth. Some of them trail horizontally beneath 

 the surface. They do not, as the foregoing, depend upon the stock of the previous year, 

 but annually produce new roots, and form new accumulations, sometimes in separate por- 

 tions of the root, as in the dahlia or in the Orchis, where, while one or more of such 

 reservoirs is exhausted each year, others are providentially formed for the next years sus- 

 tenance; and so on from year to year, a portion annually perishing, but the individual 

 plant surviving indefinitely. More commonly, the whole body and main branches of the 

 root are somewhat thickened, or portions of the stem may subserve this purpose, as in 

 all tuberous roots; or the nourishing matter may be widely distributed through the trunk, 

 as in shrubs and trees. Thus far we have only considered the primary root, or that organ 

 which originated in the embyro of the seed at germination. Adventitious buds grow from 

 most stems when placed horizontally on the ground, or buried beneath it, and this is very 

 common to some species; thus the verbena is furnished with joints at intervals of several 

 inches each, all of which strike when placed in contact with the soil. " Such roots obey 

 the ordinary tendency of the organ, avoiding the light, and seeking to bury themselves in 

 the soil. Thus when a part of the stem of a plant be cut oft" at each end, and subjected 

 to the requisite amount of light, heat, and moisture — they will in nine cases out of ten 

 take root. It is in this manner that most green-house shrubs and plants are cultivated. 

 Many plants will emit roots from their leaves. For instance, if the leaf of a Gloxinia or 

 Gesneria be pinned upon the surface of some soil placed in a pot, roots will be seen to 

 issue from the stem in the course of from four to six weeks." To this, as in every other 

 general rule, there are exceptions — as in the case of aerial roots. Such plants as the 

 Poison Ivy, (^Rhus toxicodendron,') Trumpet flower, {Teconiia radicans,') &c., emit aerial 

 rootlets from their stems, which fix them to any object which may present itself; in this 

 case the plant draws its nourishment from the soil through its roots, the aerial ones only 

 serving for mechanical support ; in this way a plant, in the course of a few years, reaches the 

 tops of the highest trees. There are other plants which produce true aerial roots, which 

 are emitted from the stem, descend to the ground and grow. This phenomena may be 

 observed in our common Indian corn, the lower joints of which often send down roots 

 the length of three and four inches; but is more perceptible in the vegetation of a south- 

 ern climate, where the atmosphere is charged with moisture for a large part of the 3'ear. 

 The Pandanus or Screw Pine, forms a good illustration. The roots are emitted from the 

 stem, and fall down, which gives the tree the appearance of having been raised out of the 

 ground. The Banyan also affords another illustration; in this case the roots spring from 

 the horizontal branches, often at a great length from the ground; they then descend, take 

 root, and produce in their turn, plants similar to themselves. This tree grows to an 

 immense size; there is one in the world, which, it is said, is suflBciently large to shelter 

 ten thousand men. The Mangrove is very similar in its habits. 



Prof. Gray says: Its aerial roots spring both from the main trunk, as in the Pandanus, 



