372 T. Holm — Triadenum Virgiiiicum (Z.) Rafin. 



developed from the axils of the lower stem-leaves, perhaps even 

 from the cotyledons. But thej are not subterranean ; they 

 bear only green leaves and have no swollen internodes, and a 

 like manner of propagation is met with in other species, for 

 instance II. jperforaturn and II tetrapterum. The rhizome 

 of Triadenum is especially characteristic, by the fact that while 

 the underground portion of the main axis stays alive for some 

 time, it never shows the swelling of the internodes as do its 

 lateral branches, at least those from the axils of the cotyledons. 

 Tuberous rhizomes are common, as we remember, but they are 

 mostly of two kinds : either is the main axis very slender and 

 develops equally slender, horizontally-creeping stolons of which 

 the outermost internodes become swollen so as to form a tuber, 

 " tuberiferous stolons," or the main axis is already at the seed- 

 ling stage visibly swollen, the swelling being moreover observ- 

 able in all the subsequent internodes, that stay underground, 

 as we remember from Sangidnaria^ Podophyllum and many 

 others; such rhizomes are called "tuberous." 



Now in regard to the root-system, Triademim possesses a 

 main root, as shown in figures 1 and 2 (R.), which persists for 

 about two seasons, when the stolons break oif from the mother 

 plant and develop adventitious roots at the nodes '{r in figure 3), 

 or more correctly just above these. The position of these 

 adventitious roots is quite singular since they break out in a 

 very short distance above the axillary buds, one above each, 

 and when the buds stay dormant, the roots appear as if they 

 were axillary ; these roots are endogenous. This position of 

 adventitious roots is not frequently met with, and we might 

 recall some of the earlier observations upon this subject. 

 Most frequently secondary roots develop at the nodes of stems, 

 and when the leaves are opposite (and the stem quadrangular ?) 

 there may be observed four such roots at each node, one on 

 each side of the leaf-base, or there may be several, as in a num- 

 ber of Gra-minem^ JuncacecB., Ranuiicidacem^ Umhelliferce^ etc. 



Irmisch found from one to four secondary roots above the 

 axillary bud in certain species of Pyrola ; Professor Warming 

 observed a similar position of such roots in Hottonia^ Pentaria, 

 Cardainine, iSediiTn^ various species of Campanida^ etc. In 

 Pyrola aphylla, which we have described in a previously 

 published paper, the adventitious roots do not break out exactly 

 above the buds, but a little to the right or left of these. 



But in Triadenum. we observed only one root above each 

 bud, two at each node, although the leaves are opposite ; we 

 must not forget, however, to state that the stem is cylindrical 

 in this genus. 



While thus the subterranean organs of Triadenum offer 

 several points of interest, and by which the genus shows a 



