1915] CURRENT LITERATURE 499 
functional cotyledon. The absence of a vascular strand in the smaller cotyle- 
don has been used as evidence to prove that it is not a second cotyledon. The 
reviewer has no doubt that when a relatively great quantity of material shall 
have been studied a procambium will occasionally be found in the second 
cotyledon. It is unfortunately the habit of some investigators to make 
sweeping conclusions from an examination of a very small quantity of material. 
The facts shown by this reinvestigation of the grasses are as follows: 
“The terminal cell of the proembryo forms a group of cells; the peripheral 
cells of the group develop the cotyledonary ring or sheath, on which two grow- 
ing points appear. One of these growing points soon ceases to be active, and 
the whole zone develops in connection with the other growing point; but at the 
base of the growing cotyledon a notch is left by the checking of the growing 
point. This notch is really the space between the two very unequal cotyledons 
which surround the real apex of the embryo. The apex of the embryo is at 
the bottom of the notch, and not at the tip of the large embryo. This apex 
soon begins to form leaves, and the so-called stem tip appears issuing from the 
bottom of the notch, in a relation apparently lateral only because the two 
cotyledons are so unequal. Furthermore, when the stem tip is examined, it is 
found not to be a stem tip, but a cluster of leaves, whose rapid development 
has aborted one of the growing points on the cotyledonary zone. All this is 
very obvious in grasses and is equally obvious in si ocsegae proembryo, but 
it escaped the earlier observers of filamentous proembryo 
The general conclusion is that “monocot eiess Is sinh one expression 
of a process common to all cotyledony, gradually derived from see 
and involving no abrupt transfer of a lateral structure to a terminal origin 
Anatomy of Helminthostachys.—In the third of his series of papers on the 
Ophioglossaceae, LANG" gives the results of a reinvestigation of the anatomy 
of the rhizome of Helminthostachys, together with the details of the vascular 
connections of two branching specimens. In rhizomes of young plants, the 
xylem forms a solid strand of two kinds of tracheids; those of the outer part 
having pitted walls, while the inner elements are smaller and are spirally 
thickened. By comparison with the bases of branch steles, where a similar 
condition exists, and by examination of the origin of leaf traces, where the 
protoxylem becomes evident, it is shown that the two kinds of elements in the 
juvenile type of stele are outer and inner metaxylem, respectively; and that 
therefore the stele of Helminthostachys is mesarch even in the juvenile condition. 
The transition to the adult condition begins by the appearance of parenchyma 
cells among the tracheids of the inner metaxylem, thus forming a mixed pith. 
In the adult condition the stele is greatly expanded and the pith is large. 
1 LANG, Witt1aM H., Studies in the morphology and anatomy of the Ophio- 
glossaceae. III. Onthe anatomy and branching of he rhizome of Helminthostachys 
Janica. Ann. Botany 29:1-54. pls. 1-3. figs. 7. 
