DICOTYLEDONS. 
lie with their inner faces flat against one another (Figs. 435, 436); but are not 
un frequently folded or wrinkled and curved backwards and forwards (as in Theobroma 
with thick, Acer and Convolvulaceae, &c. with thin cotyledons) ; less often they are 
rolled spirally round one another (Fig. 434)- 
The axis of the embryo beneath the cotyledons is generally elongated and 
fusiform, and when of this shape is described in works on descriptive botany as the 
Radicle. This fusiform body consists however in its upper and usually larger part of 
the hypocotyledonary portion of the stem, and only the lower posterior terminal 
piece, which is often very short, is the rudiment of the primary root (Fig. 437). The 
rudiments of the secondary roots can sometimes be distinguished in the tissue of the 
primary root (in Cucurbita^ and according to Reinke in Impatiens). 
Fig. \-i<^.~Ricinus co7nvi7iins ; I longitudinal section of FlG. 6,1^.— Vicia Faha : A seed with one of the coty- 
the ripe seed ; // germinating seed with the cotyledons still ledons removed, c the remaining cotyledon, iv radicle, 
in the endosperm (shown more distinctly in yl and />'), plumule, j testa ; j5 germinating seed, j testa, / a por- 
j testa, e endosperm, c cotyledon, he hypocotyledonary tion of the testa torn away, n hilum, st petiole of one of 
portion of the stem, w primary root, lu' secondary root, the cotyledons, k curved portion of the axis above the 
X the caruncle, an appendage of the seed characteristic of cotyledons, he the very short hypocotyledonary portion of 
Euphorbiacese. the axis, h the primary root, tvs its apex, kfi bud in the 
axil of one of the cotyledons. 
Germination generally takes place — after the testa, or in dry indehiscent fruits 
the pericarp, has burst from the swelling of the endosperm or of the cotyledons 
themselves — by the elongation of the hypocotyledonary portion of the axis to such 
an extent as to push the radicle out of the seed, the root then beginning to grow 
rapidly and generally attaining a considerable length and forming secondary roots 
in acropetal succession, while the cotyledons and plumule still remain in the seed 
(Figs. 435, 436, 437). Thick fleshy cotyledons usually remain in the seed during 
germination, finally perishing after their food-material has been consumed (as in 
Phaseolus multiflorus, Vicia Faba, Fig. 436, Quercus, Fig. 438). In this case the 
petioles of the cotyledons lengthen so much that the plumule which is concealed 
