46 Rennert : Seeds and Seedlings of Arisaema 



soon as the hypocotyl has found its way into the ground. Seed- 

 hngs of A. Draconiiiim vary greatly also in the number and kinds 

 of roots which they send forth. Those with the most well de- 

 veloped system have two primary roots from the base of the 

 hypocotyl and later a thick root arising adventitiously from the 

 the nodes. This secondary root, becomes contractile and trans- 

 versely ridged for part of its length. One of the primary roots 

 also often becomes contractile and helps to draw the corm deeper 

 in the ground. A secondary root, however, is developed only in 

 those seedlings which also send up a plumule and a few even of 

 these have none. The seedlings in which the plumule has not 

 started into activity have as a rule two primary roots, one of which 

 becomes thickened and assumes the function of contraction. In 

 some cases neither of the primary roots is contractile and in others 

 only one short thin root is produced. A direct correlation be- 

 tween leaf and root development is here evident. Variations in 

 the structure as well as the number of the roots occur. The con- 

 tractile roots which are for the most part simple have been ob- 

 served occasionally to be branched. In another instance (the 

 single case in which two contractile roots occurred in the lot of 

 A. Dracontiinn seedlings observed) two contractile roots were fused 

 for part of their length. The root system oi A. tripliylhnn is very 

 much better developed than is that of A. Dracoiitmm, for the roots 

 are both longer and more numerous. The seedlings have always 

 two and often three primary roots which reach a length of 5 cm. 

 and in addition after the seedling is well under way, three thick 

 adventitious roots appear, budding from the nodes. These roots 

 are contractile and show the same transverse ridges as the con- 

 tractile roots of A. Dracontium. In some cases they pull the 

 hypocotyl down as much as 2 or 3 cm. below the level at which it 

 germinated. After the secondary roots become firmly established, 

 the primary roots grow no more and the greater part of the entire 

 root function is discharged by the contractile roots which bear root 

 hairs near their tips and become about 7 cm. long. 



The only difference in microscopic structure between the con- 

 tractile, secondary and primary roots consists in the greater radial 

 elongation of the cells of the inner cortex of the contractile roots. 

 In A. Dracontium the root stele of the primary root shows a diarch 



