SOLANUM TUBEROSUM 



547 



ing Solanum muricatum and Solanum tuberosum respectively, 

 have described the development of the gametophyte as being 

 similar to what was once called the "Lilium" type of development 

 in which all four megaspores remain functional and divide to 

 produce the eight-nucleate gametophyte. Studies by Bhaduri (5), 

 Cooper (8), and Schnarf (ii) indicate that the Solanaceae have 

 the usual angiospermous type of gametogenesis. 



According to Bhaduri and Soueges (xi) the presence of tapetal 

 tissue covering the embryo sac is a characteristic feature of the 

 Solanaceae, and the former found that it was derived from the 



Fig. 189. A-F, stages in development of embryo ; G, diagrammatic outline of young 

 embryo at time of differentiation of cotyledons : ca/, calyptrogen ; dgn, dermatogen ; pbm, 

 periblem ; pi, plerome ; sus, suspensor. (After Tognini, Isf. Bot. Univ. Pavia.') 



integument in all species investigated. This tissue serves the 

 dual function of secretion and absorption. 



Young (30) has reported three instances in which the ovule 

 contained two megagametophytes. In these cases, the vascular 

 strands supplying the ovule branched in the funiculus and a branch 

 was directed toward each gametophyte. 



Embryogeny. — Embryogeny in the Solanaceae has been studied 

 by several investigators including Guignard (14), Soueges (j-y), 

 Tognini (15), Ferguson (13), and Bhaduri (6). Guignard reports 

 that there is no early, free-nucleate stage in the formation of the 

 endosperm and describes double fertilization in the case of 

 Nicotiana and Datura with endosperm formation following triple 

 fusion. Ferguson, while agreeing with Guignard in respect to the 

 absence of a free nucleate stage, has demonstrated in Petunia that 

 the first divisions of the fusion nucleus occur prior to fertilization. 



