THE ENDOSPERM 229 



often show increased activity in postfertilization stages. In Agro- 

 stemma (Fig. 125) the primary endosperm nucleus, originally situated 

 just below the zygote, enters the base of the diverticulum and divides 

 to form two daughter nuclei, one remaining in the embryo sac and 

 giving rise to the bulk of the endosperm and the other passing into 

 the diverticulum. Similar diverticulae are seen in several other 

 members of the Caryophyllaceae, but the time of their appearance 

 is not the same. In Gypsophila the outgrowth originates even 

 before fertilization; in Saponaria, after the second nuclear division 

 in the endosperm; and in Melandrium, at a still later stage (Rocen, 

 1927). 



Cellular Endosperm. In the Cellular type the division of the 

 primary endosperm nucleus is followed immediately by a chambering 

 of the sac. The first wall is usually transverse but sometimes verti- 

 cal or oblique, and in a few cases the plane of division is not constant. 

 On the basis of the orientation of the walls following the first two or 

 three divisions, this type of endosperm has been classified into several 

 subtypes (see Schnarf, 1929). For our purpose, however, it will 

 suffice to refer to a few concrete examples in order to illustrate the 

 range of variation that has been reported. 



Adoxa (Lagerberg, 1909) is a well-known instance in which the 

 first as well as the second division of the endosperm mother cell is 

 vertical, resulting in the formation of four large cylindrical cells, 

 all similar to one another (Fig. 12QA-B). The third division is 

 transverse and results in eight cells arranged in two tiers (Fig. 126C). 

 The fourth division is also transverse but further divisions are 

 irregular. 



A similar orientation of the first wall is known in Scabiosa (Doll, 

 1927) and Circaeaster (Junell, 1931). In Peperomia (Johnson, 1900), 

 Centranthus (Asplund, 1920) (Fig. 126D), and Helosis (Fagerlind, 

 1938) also, the first wall is longitudinal but sometimes it may be 



Fig. 124. Stages in development of endosperm in Macadamia ternifolia (A-C) 

 and Grevillea robusta (D-G). A, Macadamia, embryo sac showing free endosperm 

 nuclei; lower end of sac is invading nutritive tissue in chalaza. B, l.s. young seed 

 showing embryo sac with upper cellular endosperm and lower free nuclear endo- 

 sperm. C, embryo sac from B, enlarged to show details of endosperm; two-celled 

 proembryo is seen at upper end of sac. D, Grevillea, l.s. ovule (diagrammatic). 



E, embryo sac from D, enlarged to show young embryo and free nuclear endosperm. 



F, l.s. young seed, showing "vermiform appendage" formed from basal part of 

 endosperm. G, whole mount of endosperm, showing vermiform appendage. (After 

 Kausik 193Sa,b.) 



