6 MINNESOTA BOTANICAL STUDIES. 



the meantime all the cells of the original row of three or four cells 

 divide lengthwise, whereby a short, more or less massive suspensor 

 is differentiated at the posterior end (Fig. 27 and 24, PI. II). As 

 growth and development of the pro-embryo proceeds, it changes 

 from club-shaped to pyriform or ovoid (Fig, 38, PI. III). The short 

 suspensor is in intimate contact with the endosperm as long as 

 the latter is intact (Fig. 19, PI. I) but as the pro-embryo rounds 

 oft' more and more and becomes larger, the suspensor begins grad- 

 ually to disappear. 



The first indication of leaf and plumule differentiation is to be 

 noted in the fonn of a small depression which forms on one side of 

 the ovoid cotyledon (pro-embryo) close to the suspensor (Fig. 

 29, PI. II). By the time this depression first becomes evident the 

 pro-embryo is already a massive body numbering thousands of 

 cells. The depression deepens and becomes a groove (Fig. 25, PI. 

 II) by the surrounding tissue growing up from below and from both 

 sides towards the middle. The two edges come close together, there- 

 by covering up the developing leaf rudiments, and form a narrow 

 slit in the surface of the pro-embryo, near the suspensor (Fig. 

 26, PI. II). The first leaf arises on the axial side of the groove, 

 appearing at first like a small protuberance. Immediately below 

 it the apex of the stem differentiates (Fig. 39, PI. Ill), and on the 

 other side of this a second leaf is formed alternating with the first. 

 The overlapping leaf rudiments are more or less sharply bent over 

 the stem apex and in sectional view appear somewhat \'"-shaped 

 (Fig. 40, PI. III). 



By this time the pro-embryo has assumed an almost spherical 

 shape, and practically all traces of the suspensor have disappeared. 

 The radicle begins to differentiate just below the suspensor region. 

 The root-cap appears as a slight elevation and beneath it the plerome 

 is distinctly traceable by the presence of a group of trachieds (Fig. 

 40, PI. III). Tbe axes of the plumule and the radicle form a some- 

 what acute angle with each other, the one being bent back upon 

 the other (Fig. 40, PI. 3). While these structures are being devel- 

 oped the embryo completely devours the endosperm, the two integ- 

 uments, and the basal portion of the ovule. No ovular tissue is 

 ultimately left except a remnant of the base of the funicle which 

 remains in more or less intimate contact with the slightly indented 

 forward end of the embryo. The embryo therefore comes to lie 



