PHANEROGAM I A. 401 



tic features : The apical growth of shoot and root is only excep- 

 tionally effected by means of a single apical cell ; the small-celled 

 meristem of the growing-point of the stem is'more or less distinctly 

 differentiated into dermatogen, periblem, and plerome ; stem and 

 root are monostelic, with but few exceptions (p. 102) ; the vascular 

 bundles of the stem are generally collateral ; both root and stem 

 generally present secondary growth in thickness (except Monoco- 

 tyledons and a few other cases) by means of a normal cambium- 

 ring ; the growing-points of the lateral roots are developed from 

 the pericycle of the parent root (see p. 134). 



The Embryoyeny of the Sporophytc. The sporophyte is 

 developed from the fertilised oosphere in the ovule. The develop- 

 ment of the embryo is not continuous, but is in two 'stages, which 

 may be conveniently distinguished as the intra-scminal and the 

 extra-seminal. The intra-seminal stage includes the whole of the 

 development which the embryo undergoes during the conversion of 

 the ovule into the ripe seed that is, during what is known as the 

 " ripening of the seed." The extra-seminal stage includes the 

 development of the embryo which follows the sowing of the seed ; 

 that is, the escape of the embryo from the seed, and the gradual 

 development of the characters of the adult plant. The interval 

 betw r een these two stages may be brief, or it may extend over many 

 years if the seed be kept dry. The " germination " of the seed 

 when sown is simply the resumption of development by the embryo 

 in consequence 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 Grymnosperms each oospore gives rise to more 

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



Generally speaking, the oospore 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 a suspensor, which bears 

 at its lower end the other cell, termed the embi-yo-cell, from which 

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

 veloped (cf. Lycop.odinse, pp. 387, 393). 



The suspensor is for the most part a temporary organ of the 

 embryo, but it frequently contributes the primary root to the 

 embryo. It commonly becomes a filament of a single row of cells. 

 Its function is, chiefly, to place the embryo in such a position 

 within the developing seed that it can easily avail itself of the 

 nutritive materials stored in the adjacent cells. 



