THE FEMALE GAMETOPHYTE 103 



regarded as indicating a primitive condition of the nutritive 

 tissue in the female gametophytes of Angiosperms ; but the 

 antipodals of many of the Compositae are organized into an 

 aggressive haustorium which can only be regarded as a very 

 specialized organ. 



The enlargement of the embryo-sac and the nature of its 

 development, both before and after fertilization, are extremely 

 varied. The enlargement is directly related to the digestion 

 of the contiguous tissue. In a few cases this destruction is not 

 extensive, and more or less of the nucellar tissue is permanent 

 (perisperm) and is used for the storage of reserve food, as in 

 the Seitamineae, Piperaceae, Chenopodiaceae, Phytolaceaceae, 

 Caryophyllaceae, Xymphaeaceae, etc. In most cases, however, 

 the destruction of the nucellar tissue is complete to the integu- 

 ment, and even that is sometimes involved, as in Allium odo- 

 rum, certain orchids, and Astilbe (Webb 111 ). Frequently the 

 tissue at the apex of the nucellus remains as a cap on the em- 

 bryo-sac, as in Arisaema (Mottier 27 ) and other Araceae, 

 Lemna (Caldwell 02 ), Liliaceae, Silphium (Merrell 77 ), ami 

 many other forms, and this is frequently accompanied by more 

 or less elongation and even division of the capping cells. 



Frequently a definite nutritive jacket invests the embryo- 

 sac, consisting of one or more layers of cells with deeply stain- 

 ing contents (Figs. 47, 50 J. For the most part this is a single 

 layer derived from the integument, but in Armeria it is derived 

 from the nucellus, and in Erodium one layer is derived from 

 the nucellus and the other from the integument. This jacket 

 has been called a tapetum, and such it is in function. In using 

 the term, however, there is danger of confusing it with the 

 tapetum of ordinary sporogenous tissue. This jacket has been 

 definitely observed as conspicuous in Helosis (Ohodat and 

 Bernard 83 ), Slum, many Scrophulariaceae (Balicka-Iwanow- 

 ska 68 ), Campanula (Barnes 18 ), Stylidaceae (Burns 85 ), and 

 certain Compositae, and by Billings 100 in numerous sympeta- 

 lous forms, among the most conspicuous being Lobelia, Primu- 

 laceae (except Lepto siphon), Linum, Forsythia, Amsonia, 

 Menyanthes, Polemoniaceae, Myoporum, Globularia, Scaevola, 

 Calendula, etc. 



In many cases the mieropylar end of the sac destroys all 

 of the nucellar tissue capping it, and protrudes more or less 

 8 



