THE ENDOSPERM 245 



that the entire tissue of the chalaza and the integument becomes 

 riddled by a number of haustorial processes. 



A very peculiar mode of development, which seems to bear no 

 relation to any of the others, occurs in several members of the Lo- 

 ranthoideae (Treub, 1885; Rauch, 1936; Schaeppi and Steindl, 1942; 

 Singh, 1950; Johri and Maheshwari 1950; Maheshwari and Singh, 

 1950). Here the primary endosperm nucleus migrates to the cha- 

 lazal end of the extremely long and tubular embryo sac. The 

 exact sequence of divisions has not been traced, but eventually the 

 whole of the comparatively broad lower portion of the embryo sac 

 becomes cellular. Cell formation gradually extends upward to the 

 point at which the embryo sac protrudes out of the ovary into the 

 style (Fig. 138). Frequently the development of the endosperm 

 and embryo is initiated in several embryo sacs. Since these lie 

 close to one another, the separating walls between them get dis- 

 solved and their endosperms fuse to form a single composite tis- 

 sue. Sometimes, the boundaries between the individual embryo 

 sacs are still distinguishable at their upper ends, although their 

 basal portions have already fused and show several embryos sur- 

 rounded by a common mass of endosperm. 



Helobial Endosperm. The Helobial type of endosperm is inter- 

 mediate between the Nuclear and the Cellular. The first division 

 of the primary endosperm nucleus results in the partition of the 

 embryo sac into two chambers, of which the micropylar is usually 

 much larger than the chalazal. Several free nuclear divisions take 

 place in the former, but in the latter either the nucleus remains 

 undivided or undergoes only a small number of divisions. Earlier 

 workers often mistook the chalazal chamber for a hypertrophied 

 antipodal cell. 



Eremurus (Stenar, 1928a) may be cited as an example of a typical 

 Helobial endosperm. The first division of the primary endosperm 

 nucleus results in the formation of two chambers, a large micropylar 

 and a small chalazal (Fig. 139 A). Free nuclear divisions occur in 

 both but are more rapid in the micropylar chamber (Fig. 139 B-D). 

 Thus, when there are four nuclei in the chalazal chamber, the micro- 

 pylar has eight; when there are eight in the chalazal, the micropylar 

 has 16; and when there are 30 to 32 nuclei in the chalazal chamber, 

 the micropylar has a considerably larger number. In older ovules 

 the chalazal chamber becomes depleted of its cytoplasm and begins 



