APEX OF THE HOOT OF OSMUNDA AND TODEA. 79 
serving transverse sections of roots of irregular meristematic 
structure care must be taken to distinguish sections passing 
through the root cap, immediately above the actual initial 
cells, from those passing through the initial cells themselves. 
It is well known that investigators have at times fallen into 
error on this point. In all cases I have mounted all the 
transverse sections cut from one root on the slide together, 
and have not drawn conclusions from any one section till it 
has been compared with the other sections of the series, 
and its actual position in the original root been thereby 
defined. Though the grosser errors have, I think, been ex- 
cluded by due care on this and other points, still the difficul- 
ties arising from want of uniformity of meristemic structure 
make absolute certainty in the interpretation of sections, and 
especially of longitudinal sections, almost impossible. Errors 
of detail, both of observation and interpretation, may have 
crept in, but still the description which follows will amply show 
that the structure of the meristem of the roots in Osmunda 
and Todea may differ essentially from the type described by 
Naegeli and Leitgeb (1. c.). 
Among the many roots of Osmunda regalis which have 
been investigated, some few show a similarity in the arrange- 
ment of the meristem to the type well known for Equisetum 
and the Polvpodiacese. These will be first described. The 
most regular which has been observed is that represented in 
fig. 1 ; unfortunately, this section was not cut exactly in a 
transverse plane, and hence, as regards their form, the seg- 
mental cells are not so regular as they would otherwise have 
appeared ; still it is clear that there is in this case a three- 
sided apical cell, from the three sides of which segments i — iv 
have been cut off in regular order. It is worthy of note that 
this was one of the thinnest of all the roots from which sections 
were cut; it measured -fifths of an inch in transverse 
diameter at the level of the section : the question as to the 
relation of bulk of the root to the arrangement of the apical 
meristem will be discussed more at length below. 
Three examples of one four-sided apical cell have been 
