1899] Leavitt, — Adventitious plants of Drosera 207 
It must not be supposed, of course, that any individual leaf changes 
from rotund to binate. The forms represented are permanent. Mature 
plants, however, would not show the peculiarities now under discussion. 
The phenomenon here presented, well known in seedlings, is worth 
notice for two reasons, first because of its bearings on the probable 
affinities of the species of Drosera, and secondly from its relation to 
the problem of heredity. 
The studies of Dr. R. T. Jackson have shown stages of development 
in flowering plants, manifested in the shapes of the leaves, which are 
almost as striking from a genealogical standpoint as the steps of de- 
velopment which give rise to the embryo within the embryo-sac. Dr. 
Jackson's palaeobotanical researches have established the fact that in 
the leaves of the seedling we may often trace something of the plant's 
ancestry, in accordance with the familiar principle that ontogeny repeats 
phylogeny. The application of this generalization to the systematic 
botany of phaenogams is suggestive. 
If we may trust Dr. Jackson's conclusions, the peculiar early leaves 
of D. binata would indicate the derivation of this species from D. 
rotundifolia through a series of plants the character leaves of which 
were successively triangular, obreniform, crescent-shaped, and finally 
elongated in two parts as at the present day. 
Seedlings of D. rotundifolia have early leaves like D. anglica (a 
spatulate-leaved form), according to Sir John Lubbock ; and this would 
imply the historical priority of the latter species or type over D. ro£un- 
difolía and D. binata. 
The primitive leaves of D. fliformis (fig. 5), probably indicate the 
origin of this species from the progenitors of D. rotundifolia. 
Interpreting the vestigial foliage of the above-mentioned Drosera 
species in this way we look back to a common archetype possessing 
elongated leaves. One line of descendants has kept this character, 
another has reduced the spread of blade to a minimum, in the filiform 
condition, while a third at first shortened and expanded the blade to 
orbicular and subsequently has modified this form into the curious 
double-forked linear leaf of D. binata. 4 
With regard to the second point of interest, the young plants of D. 
binata precisely correspond to the description of the seedlings of the 
same species as given by Lubbock. The series of odd-shaped leaves 
serves to exhibit the noteworthy fact that individuals adventitiously de- 
rived parallel at all stages those derived from the egg-cell. With, of 
