THE FEMALE GAMETOPHYTE 105 



it has been observed to enlarge more or less abruptly, forming 

 a bulbous chalazal haustorium. In Carina indica this becomes 

 much larger than the rest of the embryo-sac; and in Saururus 

 cernuus Johnson" 7 describes the embryo-sac as elongating rap- 

 idly, broadening below, the upper part remaining narrow, the 

 completed sac resembling a long-necked flask (Fig. 49). 



In addition to the various forms of haustorial apparatus 

 described above as developed in connection with the embryo-sac, 

 certain extreme cases deserve special mention. It has long 

 been known that among the Santalaceae (Santalum, Thesium, 

 Usyris, etc.) the embryo-sac develops a micropylar tube that 

 passes through the micropyle and enters the cavity of the ovary, 

 and that in some of them {Thesium, etc.) there is also an antip- 

 odal tube (see Guignard 17 ). These remarkable tubular or 

 vermiform haustoria obtain nutritive material beyond the ovule. 

 Later, Johnson 22 described in detail the haustorial apparatus 

 of Myzodendron, another genus of Santalaceae. The young sac 

 is broad above and narrowed toward the antipodal end. After 

 fertilization the antipodal region develops rapidly, penetrates 

 the chalaza, enters the placental axis, and curving passes down 

 it to the base of the flower, where its tip dilates and becomes 

 embedded in the " vascular cup " formed by the three diverging 

 carpellary bundles. Rigidity is given to this remarkably elon- 

 gated tube by numerous cross-walls, but these are lacking in the 

 placental region. 



Among the Amentiferae (Miss Benson 31 ) vermiform caeca 

 are often sent out from the embryo-sac. In Fagus sylvatica 

 this tubular outgrowth penetrates to the base of the nucellus, 

 the primary endosperm nucleus passing into it, but not the 

 antipodals, which are anchored by thick walls. In Castanea 

 vulgaris the caecum develops from the side of the sac just above 

 the narrow antipodal prolongation, is entered by the endosperm 

 nucleus, and passes down between the nucellus and the integu- 

 ment. In Cur [>in us Betulus the chalazal region is sometimes 

 riddled by the long caeca from the several embryo-sacs; and in 

 Corylus Avellana a short caecum appears after fertilization. 



In Casuarina, as shown by Frye, 139 a conspicuous vermi- 

 form caecum is developed much as among the Amentiferae. 

 From the antipodal extremity of the sac a long tube penetrates 

 the chalazal region, into which the endosperm nucleus passes 



