ORDER OF DEVELOPMENT 



159 



recognized, the one having its branches and leaves so disposed as to 

 conduct the rain which falls upon them in toward and down the stem, 

 the other conducting it outward, so as to fall from the periphery. An 

 examination of the former class of plants may be expected to disclose 

 a tap-root which maintains a vertical downward direction, its branching 

 not being wide. Those of the second class will generally be found to 

 have their tap-roots quickly dividing up into numerous horizontal 

 branches which bear the greater part of their small absorbing rootlets 

 around the periphery, just where they will catch the droppings from the 

 periphery of the leafy crown. 



Fig. 437. Tubercles of Jalap. 438. Death of first portion of stem, its subsequent growtli maintained 

 by cluster of secondary roots. 439. Tap-root, with branches, of Ambrosia, 440. Underground portion 

 of potato plant: a, tubers: b, rhizomes, the roots seen intermingled. 441. A uapiform fleshy root. 

 442. Fusiform. 443. Conical. 



The "Multiple Primary Root." — If the primary root of a very young 

 plant divide at once into a number of approximately equal branches, 

 it constitutes the so-called Multiple Primary Root. This term has, 

 however, been applied to a number of root-clusters of similar appear- 

 ance, but of very dissimilar origin. In some cases the primary root 

 continues its vertical growth but does not increase in thickness to any 

 appreciable extent. A number of similar roots then develop near its 

 point of origin, so that a fascicle of similar roots at length results, as in 

 the onion. In other cases a prostrate stem takes root from one of its 

 nodes, the portion below this point (Fig. 438, a), with the original roots, 



