504 Thoday. — On the Organization of Growth and 
regions of herbaceous stems and has applied the doctrine of recapitulation. 
For instance, 1 he points to the ‘ circular and complete woody cylinder * in 
the lower region of the epicotyl and the multifasciculate structure of the 
upper region of the same plant as ‘ developmental evidence ’ pointing to the 
‘ derivation of herbaceous forms from woody ones \ Again, referring to 
Helianthus hirsutus , he says 2 that in the upper ‘ region the foliar traces, 
instead of being depressed below the level of the woody cylinder as in the 
basal region, ‘ are outstanding, a condition very commonly found in extreme 
herbs which have largely lost their woody texture \ 
Sinnott and Bailey 3 similarly say, ‘ The base of most herbaceous stems 
is much stouter than the upper portion and often shows a close resemblance 
to a woody twig. On passing upward from such a base to the more delicate 
portions ol the stem we can readily observe the progressive decrease in 
cambial activity and increase in parenchymatous tissue which have caused 
the development of the herbaceous type.’ An application of the theory of 
recapitulation seems to be implied, though elsewhere Sinnott and Bailey 
show that they regard the theory as only to be applied with caution. 
The points emphasized in the quotations are : (1) the woodiness of the 
base and the decrease in cambial activity upwards ; (2) the depression of 
the leaf-trace bundles in the lower region and their outstanding position in 
the upper region ; (3) the increasing proportion of parenchymatous 
tissue upwards. 
With regard to (2), Text-fig. 2 shows that in the lower internodes of 
Helianthus annuus , as well as in the upper, the median leaf-trace bundles 
are at first outstanding, in conformity with the decurrent leaf bases. This 
is the case even in the first epicotylar internode. They become depressed 
owing to the vigorous secondary growth of the segments on either side and 
the sluggishness of their own cambium. The more conspicuous prominence 
of the trace bundles in the upper part is an expression of their precocity 
and more vigorous growth. Even here their prominence diminishes as the 
stem grows in diameter, and, when secondary growth proceeds far enough, 
they become depressed as at the base of the stem. 
Concerning (1), the greater woodiness of the base, it is obvious that as 
the lowest internodes are the oldest they have had most time in which to 
produce secondary wood. In the case of H. annuus a comparison of the 
ontogeny of the upper and lower internodes reveals no fundamental difference 
in mode of organization. There is merely a change of scale, reflecting the 
increasing vigour of primary growth, 4 and naturally in successively younger 
internodes less and less secondary wood. Secondary growth, so far as it goes, 
always follows the same course and shows the same distribution. At the 
1 Anatomy of Woody Plants, Chicago, 1917, p. 191. 2 Ibid., p. 403. 
3 Origin and Dispersal of Herbaceous Angiosperms. Ann. Bot., xxviii, p. 559, 1914. 
4 In starved dwarf plants this increase of scale does not occur. See Text-fig. 10 (3). 
