602 COTYLEDONS. 



exhibit a remarkable agreement, but it also happens that even closely related 

 species of one and the same genus differ considerably with respect to the liberation 

 of the embryonic plant from the bondage of the seed-coat. That some idea may 

 be conveyed of the methods obtaining at germination, eight different cases will 

 be described. 



Let us begin with one of the most remarkable cases, viz. with the germination 

 of mangroves, which grow in extensive forests on the tidal swamps of tropical 

 coasts. 



The species which I select as example, and whose whole process of development 

 is clearly shown in the figures opposite, is called Rhizophora conjugata. A longi- 

 tudinal section through the pendent flower of this species (figs. 142 i'-'^'^) exhibits 

 two compartments of equal size in the ovary, and in each compartment is dis- 

 covered the commencement of a seed. After fertilization the corolla and stamens 

 fall off; the calyx remains, and the much-enlarged ovary assumes the form of a 

 stunted cone, whose apex bears two stigmas, now transformed into shrivelled 

 points. If the ovary is cut through longitudinally at this stage of development, 

 it may be seen that one compartment (fig. 142°) with its young seed is ati'ophied, 

 and the other with its seed has widened and enlarged very much. Within the 

 young seed (which is attached to one side of the originally central wall of 

 the ovary) an embryo can now be plainly distinguished, surrounded by its reserve 

 tissue. Together they fill the egg-shaped cavity, open below, formed by the thick 

 seed-coat. The embryo consists of the hypocotyl, whose free end is directed down- 

 wards, that is, towards the point of the pendent ovary, and the cotyledon which 

 forms the upper termination, tubular below, and above not unlike a Phrygian cap. 

 The cotyledon covers like an inverted bell the embiyonic bud, which is inserted 

 upon the apex of the hypocotyl. In the lower tubular portion of the cotyledon 

 are numerous vascular bundles which pass down into the hypocotyl and supply it 

 with food. A true radicle is not developed at the lower end of the hypocotyl, and 

 that which was formerly regarded as a root may be more accurately interpreted 

 as the hypocotyl itself. Strangely enough, the fruits of mangroves do not become 

 detached from the branches after the formation of the embryo; nor do they dehisce 

 to allow the seeds to fall out. On the contrary, these gei-minate while still inclosed 

 in the fruit hanging on the tree. The embryo develops within the seed-coat at 

 the cost of the reserve-food in which it is embedded, absorbing this nourishment by 

 means of the cotyledon. The whole of the exterior of the upper portion of the 

 cotyledon is covered with absorbent cells, and the materials drawn by these cells 

 from the surrounding slimy, gelatinous mass are conducted by the aforesaid 

 vascular bundles to the hypocotyl. Since, in spite of this, the amount of the food 

 stored up does not diminish, and since it is not proportioned to the size of the 

 growing embryo, it may be safely concluded that whatever food is absorbed by 

 the cotyledon, and employed for the growth of the hypocotyl, is continuously 

 replaced by the parent plant. 



When the hypocotyl has attained a length of 2 centimetres, the tubular portion 



