THE ENDOSPERM 227 



filled with cells; or there are one or two peripheral layers of cells 

 and the rest of the endosperm remains in the free nuclear state ; or 

 cell formation is restricted only to the micropylar part of the sac. 

 Sometimes all three types occur in one and the same family, e.g., 

 the Caryophyllaceae (Rocen, 1927). Not infrequently several 

 nuclei become enclosed in a cell where they may subsequently fuse 

 to form a single nucleus; or an originally uninucleate cell may be- 

 come multinucleate by divisions of its nucleus. Such variations 

 are so common that it is unnecessary to cite specific examples. 



Special mention must be made of the haustorial structures met 

 with in some members of the Proteaceae (Kausik, 1938a, b, 1942). 

 Here most of the endosperm nuclei are distributed in the upper 

 portion of the embryo sac. Cell formation is restricted to this 

 region, while the lower portion of the sac remains free nuclear. In 

 Macadamia ternifolia (Fig. 124A-C) this part forms several promi- 

 nent lobes or diverticulae which invade the nutritive tissue at the 

 chalazal end of the ovule and thus function as haustoria. It is only 

 in later stages, when the food material in the chalazal cells is com- 

 pletely used up, that the activity of these haustorial lobes comes 

 to an end. 



In another member of the Proteaceae, Grevillea robusta (Fig. 

 124ZM7), the lower coenocytic part of the endosperm grows in the 

 form of a coiled and tubular worm-like structure, which has been 

 aptly designated as the "vermiform appendage." It serves as a 

 haustorium of a very aggressive type whose coils invade the cells 

 of the chalaza and bring about their virtual dissolution. Later, the 

 appendage becomes partitioned into several large chambers which 

 undergo further subdivisions into smaller units, so that the cells 

 formed in this way constitute a kind of secondary endosperm tissue. 

 The reason why the vermiform appendage had been missed by 

 earlier workers is that they used only sections, which fail to give any 

 clear or complete picture of this organ, while Kausik used both 

 sections and whole mounts and was therefore able to give a very 

 thorough account of its development and organization. Using a 

 similar technique, Anantaswamy Rau (1950) has found that in Cas- 

 sia tora wall formation takes place only in the micropylar part of 

 the embryo sac. The chalazal part forms a narrow tube with dense 

 cytoplasm and many free nuclei. The lower part of the tube be- 

 comes irregularly coiled and twisted to form a very efficient haus- 

 torium. 



The lateral haustoria or "diverticulae" mentioned on page 144 



