236 BOTANICAL GAZETTE [APRIL 
study must be one which involves considerable technical diffi- 
culty. This is attributable (1) to the absence of an elongated 
axis and internodes and the consequent crowding of the sporo- 
phylls, and (2) to the early appearance of the sporangium and 
the consequent difficulty of distinguishing it from the other 
meristematic tissues in which it is placed. The kinds of evidence 
on which I have relied in my interpretations may ne stated briefly 
as follows: 
I. Study was made of sporangia whose sporogenous tissue 
was already distinct and unmistakable. Then by comparisons 
with successively younger sporophylls the attempt was made to 
trace the sporangium to its earliest rudiment. 
2. A careful comparison was made of sections in the three 
planes, longitudinal, transverse, and tangential. This involved 
the waste of a great deal of material. For it will be made clear 
by a glance at fig. ¢ that sections made longitudinal to the stem 
could give longitudinal sections of very few young leaves, and 
oftener than not would fail in this altogether, since the leaves 
have a spiral arrangement ; while, in order to obtain transverse 
and tangential sections, one must cut obliquely to the stem with- 
out possessing any clue by which to determine the proper angle 
of obliquity. 
3. The position of the vascular bundle enables one to 
determine whether the sections are truly longitudinal, and which 
of a number of serial longitudinal sections is exactly median. 
This help is available only after the sporangium is distinctly out- 
lined, and somewhat advanced in development, for in case of 
very early stages of the sporangium, the vascular bundle has not 
yet been differentiated. 
4. In such early stages one must depend very largely upo? 
the ligule, which in position and outline is so definite, and in 
manner of growth so regular as to make it of the highest impor 
tance in assisting one to orient the sections. 
5. The ‘Sporogenous tissue is often distinguishable from 
vegetative tissue by a difference in staining. There are three 
periods when this difference is most manifest. The superficial 
