OF CEYLON AND INDIA. 
411 
form proper primary roots. A very large number of plants, 
as is well known, show such a development of adventitious 
roots, especially Monocotyledons and water plants. 
The question then arises, whether an organ of “ root ” 
structure (i.e., in general possessing the morphological and 
anatomical features of true roots, such as the presence of cap, 
absence of leaves, endogenous branching, centripetal primary 
xylem, &c.), developed endogenously and laterally at the 
base of the hypocotyl, is really a root. It is evident that it 
cannot be regarded as strictly homologous with the true 
primary root developed from the embryo, nor with roots 
which arise as branches of the primary root. No one, how- 
ever, denies the title root to such growths, though it is 
usually qualified by the adjective “ adventitious,” and we 
perhaps hardly know their phylogenetic morphological value. 
It is every day becoming more clearly recognized"" that there 
is much less of strict homology among the organs of plants 
than has hitherto been supposed, and that just as the evolu- 
tionary tree of the various groups of plants themselves is 
now constantly requiring pollarding (to quote a well known 
morphologist), or even perhaps coppicing, so too the organs 
found among plants may have arisen by many different lines 
of development, and that it ,is almost as difficult to fix the 
morphological value of an organ as to fix the systematic 
position of a plant, on a phylogenetic basis. 
To prove the absolute root ” nature, then, of these thalli, 
is by no means easy, especially as we have not yet quite* 
decided what is a root. We ought, to prove the homology 
of primary root and adventitious root, to trace back the 
phytogeny of each, till we find the two lines unite, by one 
developing from the other, or both from some parent form. 
In the absence of any clear knowledge of the phytogeny of the 
various groups of plants which we unite under Pteridophy ta 
and Spermaphyta we cannot at present do this with any 
accuracy. But so long as we regard as roots the organs 
cf. Bower, Presidential Address to Botanical Section, British 
Assoc., Bristol, 1898, 
( 55 ) 
