1 20 Smith on Structure and Parasitism 



Plate XV, Fig. 4, shows the stage immediately following. 

 The &%% has divided longitudinally, and the suspensor consists 

 of four cells. The lowest of these is destined to become the 

 hypophysis of the future embryo. 



In Fig. 5 the &%g has divided into octants, and the hypophysis 

 is plainly marked. The suspensor is still four-celled. The 

 endosperm has increased greatly in bulk, and numerous small 

 starch grains are found in its cells. 



Fig. 6, of Plate XV, illustrates an almost mature seed. 

 The integuments have become thin and flattened, and the endo- 

 sperm contains much starch. The embryo has attained its 

 full development. The regions are not clearly marked out, 

 but the hypophysis here shows only anticlinal divisions. This 

 is in harmony with Koch's statement that the primary root 

 forms no root-cap. 



Summary. 



1. Aphyllon uniflorum is parasitic on Aster corymbosum. 

 The degeneration attendant upon its parasitic habit is expressed 



by : 



[a) Absence of chlorophyl. 



{U) Degeneration of bract-leaves. 



{c) Loss of root-hairs. 



{d) Reduction of the bundle-system, and the greater 

 relative development of phloem than of xylem. 



{e) Small size of seed and primitive embryo, and the 

 development of this embryo within a mass of pre- 

 cocious endosperm which completely surrounds 

 the embryo and suspensor. 



2. Parasitic roots form intimate connections with host-roots, 

 but the host-roots are not entirely starved beyond the point 

 of attachment. 



3. Stomata are present on bract-leaves, flower-stalk, calyx 



and corolla. 



