CHAP. II. 
EMBRYO. 
251 
and, 4., in their mequality, A cohesion of the cotyledons takes 
place in those embryos which Gaertner called pseudomonocoty- 
Jedonous^ and Richard macrocephalous. In the Horsechestnut, 
the embryo consists of a homogeneous undivided mass, with 
a curved horn-like prolongation, of one side directed towards 
the hilum. If a section be made in the direction of the axis 
of the horn-like prolongation, through the whole mass of the 
embryo, a slit will be observable above the middle of the 
horn, at the base of which lies a little conical body. In this 
embryo the slit indicates the division between the two bases 
of a pair of opposite confluent cotyledons ; the conical body is 
the plumule, and the horn-like prolongation is the radicle. 
In Castanea nearly the same structure exists, except that the 
radicle, instead of being curved and exserted, is straight, and 
enclosed within the projecting base of the two cotyledons; 
and in Tropaeolum, which is very similar to Castanea in 
structure, the 'bases of the cotyledons, are slit into four little 
teeth enclosing the radicle. The germination of these seeds 
indicates more clearly that the cotyledonary body consists of 
two and not of one cotyledon ; at that time the bases of the 
cotyledons, which had been previously scarcely visible, sepa- 
rate and lengthen, so as to extricate the radicle and plumule 
from the testa, within which they had been confined. 
In number the cotyledons vary from two to a much more 
considerable number, four occur in Boraginaceae, Brassicacese 
and elsewhere ; in Coniferae they vary from two to more than 
twelve. 
Instances of the absence of cotyledons occur, I. in Cuscuta 
(Plate VI. fig. 19.), to which they may be supposed to be 
deficient in consequence of the absence of leaves in that 
genus; 2. in Lentibulaceae; and, 3., in Cyclamen, in which the 
radicle enlarges exceedingly. To these a fourth instance has 
by some been added in Lecythis, of which Richard gives the 
following account: — The kernel is a fleshy almond-like body, 
so solid and homogeneous that it is extremely difficult to dis- 
cover its two extremities until germination takes place: at 
that period one of the ends forms a little protuberance, which 
subsequently bursts through the integuments of the seed, and 
extends itself as a root; the other end produces a scaly plu- 
