COTYLEDONS. 



603 



of the cotyledon also extends and pushes the hypocotyl in front of it until the 

 apex has bored its way through the wall of the fruit and come out into the day- 

 light (see figs. 142 .. *). The hypocotyl now elongates in a month to about 

 4 cm., and in from 7 to 9 months attains a length of 30-50 cm., and from 1-5 cm 



Fig. 142. Rhizophora conjugata. 



i Flower, cut in half longitudinally, a Fruit. Twig with two fruits, whose conical ends have been broken through by the 

 pressure of the elongating hypocotyls. * Longitudinal section through the ovary; about twice the natural size. Longi- 

 tudinal section through a fruit; the cap-like cotyledon surrounded by reserve-tissue; the lower end of the hypocotyl 

 having grown through the seed-coat has reached the lower hollow conical apex of the pericarp. Longitudinal section 

 through a fruit two months later; the tubular sheath of the cotyledon has elongated and pushed the hypocotyl quite out 

 of the pericarp. 1 Longitudinal section through a fruit eight months later. The hypocotyl is separating from the tubular 

 portion of the cotyledon, a p a rt of the same ; slightly magnified. 9 Upper end of the hypocotyl with the embryonic bud. 

 The two lowest-leaves of the bud are expanding, the two upper are still folded together. 



in thickness. It is thickest in its lower third, and is there slightly curved. Its 

 weight now amounts to almost 80 grammes. These long heavy hypocotyls pro- 

 jecting from the fruits sway to and fro with every breath of wind. At length the 

 vascular bundles, by which the connection with the tubular portion of the cotyledon 

 was retained, are ruptured (see figs. 142 7 and 142 8 ). The embryo falls away, and 



