420 Hill . — Studies in Seed Germination. 
opposite one another. One of these, which has already functioned as the 
absorbent organ in the seed, quickly develops its lamina and becomes an 
assimilating leaf, while the other remains in a rudimentary condition and is 
a scarcely visible, curved protuberance. The single assimilating organ or 
cotyledonary lamina is usually more or less cordate in outline with a well- 
marked notched apex, and is borne on a stout petiole. The cotyledonary 
petiole is slightly concavo- or plano-convex, a shallow groove or furrow 
being noticeable on the flattened inner or adaxial side, and it is from the 
edges of this groove — the adaxial ridges— -that new laminae may be 
regenerated. Under normal conditions the Cyclamen seedling remains iir 
this one-leaf stage for some time and the other 
rudimentary organ (the second cotyledon) ultimately 
shrivels and dies. When a second green leaf does 
develop under normal conditions in due course, it is 
seen to differ from the seed-leaf in the shape of its 
lamina and in the character of its margin and 
markings. Moreover this second leaf does not arise 
opposite to the seed-leaf, the rudimentary aborted 
organ being in that position, but is placed between 
and at right angles to the two embryonic structures. 
This second leaf which springs from the plumular 
axis is thus seen to be the first leaf of the plumule or 
shoot. The suppression of the short axis, owing to 
the geophilous habit of the genus and the con- 
sequent crowding of the developing plumular leaves, 
may have led to the divergent views which have 
found expression as to the morphological nature of the Cyclamen seedling. 
The seedling at this stage may be compared to that of Abronia 
(Nyctagineaceae), where in the embryo and on germination only one 
cotyledon is in evidence, the other being represented by a minute and very 
slightly developed organ. 1 
The evidence as to the morphological nature of the second green leaf 
of Cyclamen afforded by its position receives some support when the 
anatomical structure of its petiole is compared with that of the cotyledons. 
Even then doubts have been expressed as to the true character of this 
normally developed second leaf ; but these, it is hoped, may now be con- 
sidered to be finally settled by the regeneration experiments on cotyle- 
donary and plumular leaves described in the following pages. 
The development of the rudimentary curved organ at the apex of the 
hypocotyl — the rudiment of the second cotyledon — may be induced, as 
1 See Lubbock : On Seedlings, vol. i, p. 31, Fig. 64 ; he figures the embryos of Abronia arenaria 
and A. umbellata. According to Jepson, Gray, and Brewer, Botany of California, vol. ii, p. 3, the 
embryo in the genus Abronia is ‘by abortion monocotyledonous ’ . In Allionia , the next genus, the 
embryo is described as being plicate, the inner cotyledon being shorter than the outer. 
Text- fig. 1. Cyclamen 
neapolitanu? 7 i. A germi- 
nating seed, showing the 
cotyledon petiole, c. 1, and 
the rudiment of the second 
cotyledon, c. 2. 
