Differentiation in the Stem of the Sttnflower . 503 
secondary growth and produces a woody base closely resembling the stem 
of a woody plant. The approximation of the structure of the starved plant 
to that of an extreme annual is suggestive. With it may be compared 
Sinnott and Bailey’s generalization 1 ‘ that an herbaceous stem, in all its 
Text-fig. io. Sections of the stem of a starved dwarf plant already flowering, (i) First 
epicotylar internode (contrast Fig. 4, Plate XVII). (2) Third internode (cf. Text-figs. 1 and 2). 
(3) Sixth internode, near the capitulum. Endodermis dotted; the broken line indicates the 
boundary of the perimedullary lignified parenchyma ; secondary wood cross-hatched (mainly fibres). 
essentials, is like the first annual ring of its woody relatives ’. It is not 
inconceivable that a shortening of ontogeny might gradually result from 
a change of climate or migration to a less favourable habitat through physio- 
logical effects analogous to starvation without any fundamental morphological 
change. 
Discussion. 
Phylogenetic interpretations and ontogenetic stages. The structure of 
herbaceous stems has received a considerable amount of attention within 
recent years from anatomists who have sought evidences of the evolution 
of herbaceous from woody types and have endeavoured to interpret this 
evolution as a progressive adaptation to a shortened life-cycle. 
One class of anatomical evidence adduced is that derived from a com- 
parison of upper and lower regions of the same stem, on the assumption 
that the base retains ancestral features. Such a comparison does not by 
itself provide adequate data regarding the ontogeny of a stem, for each 
region has its own ontogeny. The method adopted in the present study of 
the Sunflower, of comparing the same region of the stem in similar individuals 
of different age, provides the means of testing, in a particular example, the 
validity of evidence of the kind referred to. 
Jeffrey has emphasized the differences between the upper and lower 
1 Origin and Dispersal of Herbaceous Angiosperms. Ann. Bot., xxviii, p. 559, 1914. 
