the Adventitious Leaves of Cyclamen . 437 
the phenomenon in Cyclamen should probably not be regarded as primarily 
connected with the tuberous nature of the hypocotyl. 
Reference may also be made to the exogenous roots formed in con- 
nexion with the axillary buds on the stem of Nasturtium officinale d Here 
again vascular strands are developed from cortical tissue, but the tissue 
concerned is not mature as in Cyclamen , the mode of differentiation of the 
vascular elements being comparable to that occurring in the development 
of normal primary vascular tissue. 
Among the results obtained, the most interesting are those connected 
with the origin of the adventitious leaves. The latter, to summarize, may 
be produced : (1) strictly exogenously, when there is no periderm, or 
(2) just below the cork, when periderm has been formed, or (3) beneath the 
cut surface, even from cortical cells quite near the stele. In the first case 
the epidermis of the leaf is derived from that of the tuber, while in the 
second it is subepidermal in origin. 
1 Lemaire : Recherches sur l’origine et le developpement des racines laterales. Ann. Sci. Nat., 
Bot., 7 e ser., t. iii, p. 237. 
