LYCOPERSICUM ESCULENTUM 



563 



inner cells of the integument elongate perpendicularly to the sur- 

 face of the gametophyte, forming a nutritive layer that has been 

 inaccurately designated as a "tapetum." 



Embryogeny. — Soueges (31, 3i) and Tognini (34) have given 

 detailed accounts of the embryogeny of several species of Solana- 

 ceae, and Lycopersicum has been investigated recently by Smith 

 (yf). Following fertilization, the zygote divides transversely to 

 form a two-celled embryo; and transverse divisions of these two 



Fig. 2.95. A, fertilized egg or zygote 54 hours after pollination; B, two-celled embryo; 

 C, four-celled embryo, no hours after pollination ; D, eight-nucleate embryo, 114 hours after 

 pollination; £, embryo in which dermatogen cells are cut off in tiers a and h, 130 hours 

 after pollination; F, embryo with dermatogen, periblem, and plerome differentiated, 2.2.4 

 hours after pollination (letters a, b, c, and d refer to four tiers or regions of development in 

 embryo, described in text); G, portion of longisection of ovule showing development of 

 embryo, endosperm, and inner layer of integument, same age as f ; H, longisection of basal 

 end of embryo when fruit is about 50 mm. in diameter, showing development of histogens : 

 dgn, dermatogen; emb, embryo; end, endosperm; /' int, inner layer of integument; pbtn, 

 periblem; pbm in, periblem initials; pi, plerome; r c, root cap. (Redrawn after Smith, 

 Cornell Agr. Exp. Sta. Mem?) 



cells, a and b, result in the formation of a four-celled embryo with 

 its cells in linear arrangement. (Fig. 195, A, B, C) Smith found 

 two-celled embryos about 44 hours after fertilization, and the 

 four-celled stage after no hours. From this linear series of four 

 cells, the ontogeny of the embryo follows a regular and uniform 

 sequence in most of the Solanaceae. The apical cell, a, gives rise 

 to the cotyledons; cell b produces the hypocotyl and primary 

 root; the root cap and part of the suspensor come from cell c, and 



