28 P, ORPEN BOWER. 
Cucurbitacez, there has been described, by M. Ch. Flahault,' 
a lateral structure, the account of which, given by him, 
shows that it is the morphological equivalent of the feeder 
of Welwitschia. M. Flahault ascribes to it simply the 
mechanical function of assisting the escape of the cotyledons 
from the testa. Since the seeds are exalbuminous this is 
not surprising. 
A similar structure is also described by him in Mirabilis 
jalapa. Though in this case the seed is albuminous, still 
M. Flahault ascribes to the lateral organ a mechanical 
function only, as in the case of its homologue in the exal- 
buminous seeds of the Cucurbitaceze. Darwin? gives further 
experiments, with figures, on this “ heel or peg” mentioning 
other plants (Mimosa pudica, Abronia umbellata) in which 
similar structures are formed. In none of these cases, how- 
ever, is a function ascribed to the peg, similar to that in 
Welwitschia. Regarding the case of Welwitschia from a 
mechanical point of view, it is evident that here the func- 
tion of helping the cotyledons to liberate themselves from 
the testa is more perfectly performed than in the cases des- 
cribed by Darwin, since here the hold of the feeder on the 
endosperm and testa is much more firm. 
We have now noticed a number of plants in which occur 
outgrowths of the hypo-cotyledonary stem, having the same 
morphological value. In the light, however, of the facts 
brought forward by Darwin (loc. cit., p. 104), regarding the 
inconstancy of the presence of the peg in the Cucurbitacee, 
and indeed of emergencies generally, it seems improbable 
that we have here a case of survival of an ancient form, 
but rather of individual adaptation. 
The peculiarity in the arrangement of the fibro-vascular 
bundles of the hypo-cotyledonary stem is easily put in rela- 
tion to the bundle system of other plants. 
The transition from the stem type to the root type of 
bundle is effected in most plants by a double process, the two 
parts of which are, in most plants, nearly simultaneous. 
They are (1) arotation of at least a part of each bundle on its 
axis ; (2) a separation of the phloem from the xylem (accom- 
panied or not by splittings and fusions). In Welwitschia 
the two parts of the change are distinct and separate. The 
first (¢. e. rotation of the bundles on their axes) oceurs imme- 
diately below the junction of the bundles from the plumule 
and cotyledons, while the latter (i. e. fusion of phloem and 
xylem) is effected approximately at the point where the true 
1 «Bulletin Soe. Bot. de France,’ vol. 24, p. 201, 1877. 
2 «The Movements of Plants,’ 1880, p. 102. 
