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™™ in length 
and about 4™™ in diameter. The hypocotyl (fig. 1) is comparatively 
very short, being about 5™™ 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 (Lx) embraces the inner and next younger 
one (L,), which in turn often embraces a third (L,); and finally 
beneath them all is the stem tip (sé), On the oldest leaf primordia are 
all the rudiments of the pinnae (fm) 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 r to g according to age. 
The cotyledons (cof) are apparently exactly opposite; z 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 z 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 
*Pposite 3, and again the sheathing base is more slender and folds 
‘found the next inner leaves more on that side toward which the 
‘piral turns. In the rest of the series the spiral is uniform, and the 
*verlapping more conspicuous. 
- ANTERNAL stRUCTURE.—The bulk of the embryo is of course 
