THE EMBRYO 293 



Cytisus (Fig. 16522) the suspensor cells are large and spherical and 

 appear like a bunch of grapes. 



During recent years more detailed accounts have appeared of the 

 embryogeny of the Leguminosae, 7 of which Pisum sativum (Cooper, 

 1938) may be referred to very briefly. The zygote divides trans- 

 versely into two cells, of which the basal divides vertically to form 

 two suspensor cells and the other divides transversely to form a 

 middle cell and a terminal cell (Fig. 166A-D). The nuclei of the 

 two basal cells now divide without wall formation and the middle 

 cell becomes vertically partitioned by a wall placed at right angles 

 to that separating the two basal cells. At the same time the ter- 

 minal cell divides by an oblique wall (Fig. 16QF,G). Hereafter 

 the basal cells undergo much elongation and their nuclei as well as 

 those of the middle or subbasal cells undergo a series of free nuclear 

 divisions (Fig. 16622-J"). Eventually the basal cells have as many 

 as 64 nuclei and the subbasal cells have 32 nuclei each. A longi- 

 tudinal section of the ovule cut at this stage shows a free nuclear 

 endosperm, a globular embryo, and the four multinucleate suspensor 

 cells (Fig. 16620. 



The suspensor haustoria of some members of the Rubiaceae have 

 been well known since the days of Hofmeister (1858). Lloyd (1902) 

 and Soueges (1925) gave further details of their origin and structure. 

 At first the suspensor is merely a filament of cells, but later the 

 micropylar cells send out lateral protrusions which penetrate into 

 the endosperm and swell at their distal ends (Fig. 167). Llo}'d was 

 so impressed by their appearance that he remarked: "The function 

 of the suspensor in these forms is therefore not alone to bring the 

 embryo into favorable position with relation to the food supply in a 

 mechanical sense, but to act as a temporary embryonic root." 

 Fagerlind's (1937) work seems to indicate, however, that the sus- 



7 See especially Soueges (1946c-o ; 1947a, b; 1948). 



about 20 pairs of cells; outside embryo are nuclei of endosperm. D, Phaseolus 

 multiflorus; large massive suspensor, whose cells grade imperceptibly into those of 

 embryo proper. E,F, Pisum sativum and Orobus angustifolius; suspensor composed 

 of large multinucleate cells. G, Cicer arietinum, biseriate suspensor. H, Cytisus 

 laburnum; suspensor appearing like bunch of grapes; embryo showing initiation of 

 two cotyledons. I, Ononis fruticosa, suspensor composed of a row of seven large 

 cells, each with a single prominent nucleus and many starch grains. (After Guig- 

 nard, 1SF2.) 



