Development of Cassytha filiformis, L. 403 



ening takes place to a considerable extent throughout, but 

 continues very rapidly at the upper end, so that in the ripe 

 fruit a great cap of dense cellulose covers the upper end, four 

 times the thickness of the cap produced by the inner layer 

 of mesocarp. The cells have now become exceedingly nar- 

 row, with faint, disintegrating nuclei in the middle, the rest 

 of the cell being filled with cellulose. While the inner meso- 

 carp cells are usually quite brown in color, the endocarp is 

 lemon yellow. These two layers, particularly the inner, 

 invest the soft parts beneath with an armor of cellulose, 

 which must be an excellent protection from all ordinary 

 mechanical dangers. The only interruption to this is the 

 minute aperture of the micropyle, which is filled with cellular 

 tissue that will be referred to again. This aperture at the 

 upper end has the radicle of the embryo extending vertically 

 down from it and lying with the thicker or radicular end 

 toward it, as shown in Fig. 2. 



Internal to the horny cap is the outer indusial layer. It 

 shows rather large columnar cells, very delicate-walled and 

 empty (9). It fades out toward the micropyle. Within it, 

 in a lateral position and almost or quite absent at the two 

 poles, are several layers of loose, thin-walled empty cells 

 (10), the tegmen. By the growth of the embryo these are 

 crowded and partially absorbed until they leave only an 

 irregular thin lamellated layer pressed close to the testa. 



Next to the embryo, and separated from it by a mere base- 

 ment membrane, is a series of obliquely placed spiral cells 

 (11). These seem to form a very copious raphe and com- 

 pletely enclose the embryo. In the ripe seed they become 

 narrowed toward the base. At the micropylar end they give 

 way to a strand of fibrous tissue, which completely plugs up 

 the end of the micropyle left by the fruit and seed coats. 

 This strand extends down one side through the middle of the 

 cellular tissue of the sorus. It is directly continuous with 

 the style of the flower. 



The embryo in the ripe seed is a globular yellow body 



