RECHERCHES SUR LE TRADESCANTIA VIRGINICA. 229 
of Pteridophyte stems cannot be understood without reference to 
which descriptive anatomy is a necessary basis—we bn the 
fascinating and difficult subject of mn Heel anatomy—the 
aetrib of the different tissue systems throughout the sree plant 
§ even more obviously an essential preliminary. We cannot hope 
to arrive at trustworthy results without a most minute i accurate 
knowledge of the distribution of tissues and their elements in the 
adult = and in all stages of growth. 
abric of our anatomical knowled e has not been built up 
on systematic lines. After the work of the great founders, Von 
i Ww B 
Van Tieghem, had placed the subject on a secure base, it has been 
added to by subsequent workers as fancy or opportunity dictated, 
and with the most various objects in view. Hence it is not surprising 
should appear in our St knowledge, gaps which are often 
do actua fea exist for settling outstanding general problems 
h 
grateful to workers like M. Gravis, who undertake the somewhat 
ungrateful task of os careful anatomical monographs of single 
plants. They give us the most valuable detailed pictures of _ 
whole of the tissue Pe of a given plant in heir r mutual ¢ 
maker of generalizations. 
may be, whatever the difficulty of finding reliable information upon 
it, we can turn to avis’s monographs i in the full confidence that 
it has not been assed over in the plants which he has investigated. 
It must not be supposed that M. Gravis confines himself to mere 
description without reference to the work of other observers. is 
reading has been exceptionally rr the bibliography of the present 
volume containing the names of no less than two hundred and ten 
works—a sufficiently 1 gaat number even in these days—and 
each section of his book is full of references to, and critical dis- 
cussions of, the works of other: In this way, as might be expected, 
there are sts few questions of general anatomical interest on which 
he fails to touch in the course of his systematic treatment of his 
ct. 
This iho treatment makes it delightfully easy to find 
what one wants on any special point, and a quick comprehension 
of the author’s erties Per is still further facilitated by twenty-two pages 
. careful résumé, Finally, we have the author’s conclusions on new 
r disputed points in forty-seven concise paragraphs. The whole 
naa is indeed a model of arrangement. 
