110 BOTANICAL GAZETTE 
form the double sheath. In older stages the base of the sheath is. 
composed of many cells in width, so that the sheath appears no longer _ 
to originate as a bifurcation of a single organ, but rather as two dis- 
tinct organs. Both organs or portions of the sheath may develop 
equally, though it more often happens that one portion becomes 
larger than the other. Occasionally, the inner scarcely develops 
all, but remains a tiny rudiment. 
The sheaths which arise in the seedling develop precisely like those 
in the mature plant and differ from them in no respect. The two 
organs that originate on the ridge of tissue, therefore, may be regarded 
without hesitation as the first sheath, and as every sheath appears i 
connection with a leaf, that leaf must be the cotyledon. From the 
section of the mature plant it will be noticed that the bases of each 
leaf and its sheath are at the same level on the axis. If a difference 
in level should occur, however, whereby the base of the sheath were 
elevated above that of the corresponding leaf, the cell growth pro- 
ducing that elevation would originate from the cortical parenchy 
lying immediately under the sheath. The parenchyma would giv 
in the embryo of Sparganium a sheath. While it does not requite # 
