1909] Seedlings op Ph.enogamous Plants. 237 



plants within the frame of biologic types, where the organs 

 of vegetative reproduction, and especially the subterranean, 

 play such an important role. We might classify the seedlings 

 in accordance with the position of the cotyledons, epigeic or 

 hypogeic, and in accordance with the function of the hypocotyl; 

 when the hypocotyl persists, the primar}^ root generally stays 

 active, but when it dies off, the root becomes replaced by second- 

 ary, which may develop from the node of the hypocotyl. Another 

 modification may be noticed in the relative development of the 

 primary root as an organ for storing nutritive matters for 

 instance, sometimes accompanied by the more or less complete 

 suppression of one of the cotyledons. Finally, the singular 

 formation of a cotyledonary tube deserves, also, attention from 

 a biologic point of view ; besides that it has been made the 

 subject of a most interesting treatise by Miss Ethel Sargant 

 for defining the comparative antiquity of Monocotyledones and 

 Dicotyledones. ' 



The most simple type of dicotyledonous seedlings is un- 

 doubtedly the one in which the primary root persists, and stays 

 as a nutritive root, and in which the main function of the hypo- 

 cotyl is to raise the cotyledons above the ground, thus exposing 

 them to the full effect of the sunlight. In this type the hypocotyl 

 is straight and attains often a considerable length, much exceed- 

 ing that of the subsequent intemodes of the seedling; moreover, 

 the hypocotyl does not increase in thickness beyond the con- 

 tinuous growth of the stele, the parenchymatic tissues remaining 

 mosth' unchanged. This type is exhibited by the majority of 

 our trees and shrubs, furthermore by most of our herbs, and is 

 evidently the most common. Some examples illustrating this 

 type of seedlings may be seen in the accompanying plate, where 

 Platanus occidentalis (Fig. 19), Liriodendron (Fig. 20), Caialpa 

 (Fig. 23), Ipomcea hederacea (Fig. 24), and Tilia Americana 

 (Fig. 25) have been drawn. These seedlings show, also, another 

 point of interest, namely, the peculiar shape of the cotyledons, 

 and the diversity in foliage when compared with the leaves of 

 the mature plants. 



As the second type, may be mentioned Claytoma megarrhiza 

 (Fig. 27). In this the seedling is very small, and has the coty- 

 ledons raised above ground by a short hypocotyl; the primary 

 root is long, and at first slender with a few ramifications, which are 

 very hairy. At this stage two leaves, succeeding the cotyledons, 

 are already ^•isible, and the seedling is now readv to winter over. 

 At the end of the first season the hypocotyl shows a distinct 

 wrinkling by which the apical bud becomes pulled down beneath 

 the surface of the ground, while the root continues its growth 



