392 Farmer and Hill. — Arrangement and Structure 
of pericyclic parenchyma. Possibly this unusual character 
should be correlated with the fact that the roots of these 
plants traverse a bulky mass of cortex before passing out 
to discharge their functions with which the normal structure is 
so obviously connected. 
The cortical parenchyma of the roots whilst still enclosed 
in the stem-tissues frequently presents a curious appearance. 
The cells are elongated and their walls exhibit very regularly 
alternating transverse bands of thickening, the bars being 
separated by wider bands of unthickened wall substance. 
The whole somewhat recalls the scalariform markings of the 
tracheids, except that the bars are rather distant and the wide 
unthickened pits are not bordered. 
Having thus considered the development and distribution 
of the vascular strands in the preceding stems, it still remains 
to attempt to correlate the structure thus elucidated more 
generally with the corresponding parts of other plants, and to 
ascertain what general conclusions, if any, can be arrived at 
as the result of our investigation. And at the outset of such 
an endeavour we are confronted by difficulties of various kinds. 
The most serious ones are occasioned by the divergent views 
which are entertained as to the ‘ typically 5 (or ‘ morpho- 
logically ’) distinct regions of the tissues themselves, but which 
nevertheless form the subject-matter out of which comparative 
estimates are derived. Moreover, we still possess surprisingly 
little accurate information as to the ontogenetic evolution 
of the variously complex tissue-arrangements which have so 
often within recent years formed the subject of anatomical 
memoirs. The unwieldy terminology that tends to further 
obscure the true relations of the vascular tissues of different 
plants to each other is also in part due to the fact, only just 
beginning to become appreciated, that certain complex types 
may originate in different ways from the non- differentiated 
embryonic tissue. We are threatened with the substitution 
of an elaborate but purely formal description of these various 
types, based on a totally inadequate knowledge as to their actual 
genesis, in the place of a rigorous appreciation of the really 
