E. Drabble. 
196 
upholders of the theory now under discussion, if they can abandon 
the endodermis at all stages as a morphological guide. And it must 
be emphatically stated that only by change in the mode of apical 
development are the successive steps from theprotostele to the dictyo- 
stele brought about. Indeed, “Von Baer’s law,” if applicable to 
the stems of plants at all—as it would very strongly appear to be— 
is carried through by progressive changes in the meristem and 
procambial tissues at the apex—apical development being the mode 
of ontogeny met with in the stems of vascular plants. Mr. Boodle 
says that apical development is of no value, because it shows no 
more than can be seen in the various regions of the mature stem. 
It at all events shows just as much, and hence, if apical development 
be of no value, neither is a comparison of the successive mature 
regions. The great faith of this school seems to rest on “ a com¬ 
parison of closely related forms ; ” undoubtedly this is an extremely 
valuable method, but the conclusions drawn therefrom do not 
necessarily bear out Mr. Boodle’s views. They just as strongly 
support the views of Dr. Jeffrey (8, 9,10, 11), or Professor Farmer (7), 
or the present writer (6). If comparative work shows one thing more 
strongly than another, it is that the only distinction to he drawn is 
that between vascular and non-vascular tissues (cf. Dr. Chandler’s 
paper on “ The ‘ Seedlings ’ of Ferns” (5). Each plant solves its own 
difficulties in its own way, though doubtless closely related plants 
generally adopt similar methods, as we should naturally expect if 
the difficulties surmounted were encountered before the segregation 
of the species in question. It would be very interesting to see how 
the supporters of this view would deal with the case recently des¬ 
cribed by Van Tiegham, of two members of the same genus in the 
Calycanthaceae , in one of which the inverted bundles lying outside 
the central cylinder are said to be of “ stelar,” in the other of 
“ extra-stelar ” origin. 
According to this theory, then, the conception of the central 
cylinder seemed to be that of an originally parenchymatous strand 
occupying the centre of the stem in which a more or less continuous 
development of conducting tissue is differentiated. How the 
cylinder is to be delimited before the development of vascular 
tissue is not very clear, since the initial stratification described by 
Hanstein admittedly fails to serve in the light of Dr. Schoute’s (12) 
results for the phanerogams and Mr. Boodle’s for the ferns. If the 
mere development of vascular tissue is all that is required 
to constitute a central cylinder, then the not infrequent develop¬ 
ment of vascular strands in the cortex associated with the paren- 
