GERMINATION AND HISTOLOGY OF WELWITSCHIA MIRABILIS. 17 
stem of the mature embryo, there was not found in the 
arrangement of the tissues any indication of this organ, or 
apparent preparation for its development; the arrangement 
of epidermis and cortical tissue being uniform all round the 
stem. 
Since my work depended upon a limited number of seeds 
only, I was not able to study the early stages of development 
of this organ as fully as I should have wished ; nor could I 
obtain anything further than the following facts : 
In a seed which had been sown three days no change 
was found in the embryo. In a seedling of twelve days, 
however, the organ was found almost fully formed (fig. 2). 
In this case the root had extended to a length of about one 
and three quarter inches. The cotyledons, though still 
enclosed in the seed, had grown to about one quarter inch 
in length. Side by side with these lay the lateral organ, 
which had already attained a length almost equal to that of 
the cotyledons. From these observations we see that the 
development of the organ is, like others of the first processes 
of germination, very rapid. 
In all cases of seeds sown flat, the position of the lateral 
organs with relation to the cotyledons, was found to be as 
represented in fig. 2. In seeds sown on edge, as soon as 
room is allowed by the extrusion of the root and thicker 
part of the hypo-cotyledonary stem, the cotyledons suffer 
torsion in the cavity of the endosperm; so that the body of 
the embryo is rotated on its axis, and thus it assumes a 
position, relatively to the direction of gravity, similar to that 
in the case of the seed sown flat. The lateral organ is 
meanwhile developed in the same position, relatively to 
the rest of the embryo, as in the former case (fig. 3). 
It always appears on that side of the stem which is made 
concave by the curving of the root downwards. Hence 
it appears that the direction of gravity, relatively to the 
germinating seed, has an indirect determining influence 
upon its position. If we consider the mature embryo, 
we shall see that the lateral organ might be formed at 
either of two points (¢.e. either of the points marked z 
in the fig. 1 8B). It depends upon the position of the seed, 
and hence upon the direction of gravity relatively to it, at 
which of these two points the development shall take place. 
As to what happens when the plane of the seed or the axis 
of the embryo is exactly vertical I have no observations 
to offer. These cases would be particularly interesting for 
comparison with Ephedra. 
1 Strasburger, ‘ Conif.,’ p. 320. 
VOL. XXI.—NEW SER. B 
