1908] THIESSEN—DIOON EDULE 361 



Observations 



THE EMBRYO 



External structure. — In the mature seed the cylindrical embryo 

 is fully two-thirds as long as the endosperm, averaging 20 mm in length 

 and about 4 mm in diameter. The hypocotyl (fig. 1) is comparatively 

 very short, being about 5 mm long, ends abruptly (very often is even 

 concave), and in the center is still attached the slender, very much 

 twisted and coiled suspensor (s). The cotyledons are free for the 

 upper four-fifths of their length, the lower fifth forming a tubular 

 sheath (sh) inclosing the leaf primordia (figs. 2, 3). One of the 

 cotyledons is slightly larger than the other, and is inserted a little 

 lower on the axis, slightly enfolding the smaller one. There are 

 generally two leaf primordia, but sometimes three. The broad base 

 of the outer or older one (L r ) embraces the inner and next younger 

 one (L 2 ), which in turn often embraces a third (L 3 ); and finally 

 beneath them all is the stem tip (si). On the oldest leaf primordia are 

 all the rudiments of the pinnae (pn) of the future leaf quite well 

 advanced; while no indication of them can be detected on the younger 

 primordia. 



To understand certain features to be described later, it is necessary 

 to note the arrangement of the earlier leaves. An older plant (fig. 7) 

 may be used as an illustration, and both scales and foliage leaves will 

 be spoken of as leaves and numbered from 1 to g according to age. 

 The cotyledons (cot) are apparently exactly opposite; 1 and 2 are 

 approximately opposite, but close observation shows that they are 

 not exactly so; also 1 and 2 are approximately at right angles to the 

 cotyledons (also fig. 2). The sheathing leaf base of 7 is a little longer 

 and more slender on the side toward which the spiral turns, and 

 folds around the inner leaf or scale a little farther than it does on the 

 other side. Leaf 3 lacks still more of being opposite 2; also the 

 corresponding edge of the sheathing base of 2 is more slender and 

 folds over 3 more than its fellow. Leaf 4 lacks still more of being 

 opposite 3, and again the sheathing base is more slender and folds 

 around the next inner leaves more on that side toward which the 

 spiral turns. In the rest of the series the spiral is uniform, and the 

 overlapping more conspicuous. 



Internal structure. — The bulk of the embrvo is of course 



