ORDER OF DEVELOPMENT 



159 



rcc'()f];nized, the one liaviiiji; its l)raiiclie.s and leaves so disposed as to 

 coiidiict the rain whieh falls upon them in toward and down the stem, 

 the other condnctinjj; it outward, so as to fall from the perijjhery. An 

 examination of the former elass of plants may be expeeted to diselose 

 a ta])-r()()t which maintains a \ertical downward direction, its branching 

 not hein^' wide. TJiose of the second class will generally he found to 

 ha\c their tajj-roots (piickly dividing u]) into innncrous horizontal 

 branches which bear the greater part of their small absorbing rootlets 

 around the perii)hery, just where they will catch the droppings from the 

 peri])hery of the leafy crown. 



Fig. 437. Tubercles of Jalap. 438. Death of first portion of stem, it.s subsequent growth maintained 

 by cluster of secondary roots. 439. Tap-root, with branches, of .4 TO6ro.sia, 440. Underground portion 

 of potato plant: a, tubers; h, rhizomes, the roots seen intermingled. 441. A napiform 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 ]\Iultiple Primary Hoot. This term has, 

 however, been applied to a number of root-dusters 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 

 a])preciable extent. A number of similar roots then develoj) near its 

 l)oiiit of origin, so that a fascicle of similar I'oots at length results, as in 

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

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



