296 



EMBRYOGENESIS IN PLANTS 



cylinder of the hypocotyl is already delimited ; and the pattern of the 

 root meristem is apparent in embryos showing cotyledon primordia. 

 The number of cells in the nucellus is still on the increase up to the 

 spherical embryo stage, but thereafter the perisperm starch begins to 

 accumulate, thus affording evidence of active translocation, probably 

 of sugars, into the ovule by way of the funiculus. 



The funiculus of the young ovule has only an incipient vascular 

 strand, yet it is able to translocate all the metabolites which are used in 



B 



Fig. 82. Dicmthiis chinensis 



Starch in ovule and seed. A, Longitudinal section of ovule (diagrammatic) with a 

 seven-nucleate embryo sac and enveloping starch-containing tissue. B, Ovule with 

 young embryo. C, Ovule with maturing embryo. (A, x 102; B, x 29; C, x 21; 



after Buell.) 



the growth of the ovule. Indeed, some starch may actually be stored in 

 the young ovule. By the time the ovum is mature, the funiculus strand 

 has become fully differentiated into xylem and phloem. The synergids, 

 the basal cell of the proembryo, and the endosperm, may all function 

 as absorbing systems and all eventually contribute to the embryonic 

 development. The partial digestion of the nucellus follows a regular 

 pattern, the micropylar region disappearing most rapidly. Indeed, a 

 kind of biochemical pattern is followed during the whole post-fertilisa- 

 tion phase, the central and controlling component being the developing 

 embryo. The large basal suspensor cell has probably an absorptive 

 function. Perotti (1913) found protein granules in it in Stellaria media 



