PHANEROGAMS. 



In order to liberate them and the phimule which lies between them from the seed, 

 the hypocotyledonary portion of the axis increases considerably in length, making 

 first of all a curve which is convex on the upper side (Fig. 404), because the coty- 

 ledons still remain in the seed while the lower end of the stem is attached by the 



root to the ground. Ultimately, by a final 

 lengthening of the hypocotyledonary portion, 

 the upper part of the axis together with the 

 cotyledons is drawn out of the seed in a 

 pendent position. The axis now straightens 

 as it continues to grow, and the cotyledons 

 expand in the air, the plumule developing 

 more completely and pushing up between 

 them. The cotyledons which thus become 

 exposed to the light usually increase rapidly 

 in size, and constitute the first green leaves 

 of the plant, which are of simple form {e.g. 

 Cruciferse, Acer, Cucurbita, Convol.vulaceas, 

 Euphorbiaceae, &c). If the seed contains an 

 endosperm, the cotyledons do not emerge till 

 after it has been absorbed (Fig. 404). ]\Iany 

 transitional forms occur between the different 

 modes of germination now described ; peculiar 

 phenomena sometimes appearing which are 

 caused by special vital conditions. In Trapa, 

 for example, the primary root is from the first 

 rudimentary, and remains altogether unde- 

 veloped ; the hypocotyledonary portion lengthens 

 considerably, curves upwards, and protrudes a 

 great number of lateral roots in rows which fix 

 the plant into the ground \ 



The further development of the young plant 

 may take place by the rapid enlargement of the 

 primary axis of the embryo. While the axis is 

 growing, generally in an upright direction, the 

 shoot which developes from the plumule be- 

 comes the primary stem of the plant, lengthen- 

 ing at the summit, and usually producing 

 weaker lateral shoots [e. g. Helianthus, Vicia, 

 Populus, Impatiens, &c.). When the main 

 stem is perennial, it sooner or later ceases to develope further at the apex, or 

 the lateral shoots nearest to the apex become equally strong. An arborescent 

 head is thus formed, the main stem or trunk becoming denuded by the dying 

 off of the lo.wer branches, or the main stem continues to grow erect as a sym- 

 podium (as in Ricinus, the lime, &c.) ; or lateral shoots are formed at an early 



Fig. 408. — Almond-seed germinating, one of the 

 cotyledons c' c" being split ; the letters as in Fig. 407, 

 i the first interiiode strongly developed. 



[See De Candolle, Organographie Vegetale, PI. 55. — Ed.] 



