GROUP IV. PHANEROGAM IA. 441 



seed be kept dry, The " germination " of the seed when sown is 

 simply the resumption of development by the embryo in conse- 

 quence of exposure to the necessary conditions of moisture, 

 warmth, etc. 



In most Phanerogams, each oospore gives rise to a single em- 

 bryo; but in most Gymnosperms each oospore gives rise to more 

 than one embryo (four or many), thus exhibiting polyembryony. 



The primary development of the embryo is either holoblastic or 

 meroblastic (see p. 13) ; meroblastic embryogeny is common among 

 Gymnosperms. 



In some exceptional cases (Cycads, Ginkgo, Ephedra) the 

 embryogeny begins with free cell-formation in the oospore (see p. 

 121). 



Generally speaking, the oospore of holoblastic plants divides 

 into two by a transverse wall : the upper of the two cells remains 

 coherent to the micropylar end of the embryo-sac and developes 

 into the suspensor, an embryonic organ which is a characteristic 

 feature of the embryogeny of Phanerogams, which bears at its 

 lower end the other cell, termed the embryo-cell, from which the 

 whole or a considerable part of the body of the embryo is de- 

 veloped. In meroblastic plants, the suspensorial cell and the 

 ernbryo-cell are developed in a somewhat similar though more 

 complicated manner, from the embryogenic portion of the oospore 

 (see Gymnosperms, p. 471). 



It is in comparatively few plants that the suspensor contributes 

 nothing to the development of the permanent members of the 

 embryo. This is necessarily the case in those plants (enumerated 

 below) in which no suspensor is developed ; it is also the case 

 in some plants in which a suspensor is present (e.g. plants 

 with massive suspensors, such as Geranium, Tropaaolum, many 

 Grasses; also most Leguminosae). Here the embryo is de- 

 veloped entirely from the embryo-cell. In some cases (Viciese, 

 Coniferae) the embryo-cell, on the other hand, contributes to the 

 elongation of the suspensor. In many cases, however, the lowest 

 cell of the suspensor contributes in part (e.g. Capsella, Fig. 286) or 

 entirely (e.g. Alisma, Fig. 287) to the construction of the embryo. 



The suspensor may be regarded, in most cases, simply as a 

 temporary organ of the embryo : but it occasionally presents such 

 a degree of independence of growth, that it assumes the character 

 rather of a proembryonic organism, making the embryogeny 

 heteroblastic, than of a mere organ (see p. 14). 



