CONSERVATISM AND VARIABILITY IN THE SEEDLING 
OF DICOTYLEDONS 
Edmund W. Sinnott 
Introduction 
Ever since the statement of the law of recapitulation by the 
zoologists attempts have been made to extend it to the plant kingdom 
and to discover, in the seedling, traces of characters which have been 
lost elsewhere in the plant and which from their constancy might be 
used as guides to relationship. External characters, particularly 
"juvenile" foliage, were at first chiefly studied, but more attention 
has latterly been paid to internal structure. Jeffrey and his students 
have investigated the secondary wood of young plants for evidences 
of conservatism. It is the structure of the actual seedling, however, 
and its still dominant primary tissues, which has engaged the atten- 
tion of most students of the subject, foremost among whom are 
members of the English school of anatomists. 
Although numerous instances have been found by these observers 
where seedling structure is useful for classification, within narrow 
limits, it must be admitted that the high degree of variability recorded 
in "type of symmetry," number of protoxylem clusters, number and 
position of primary bundles, level of transition from root structure to 
stem structure, and so on, have served in the minds of many to cast 
doubt on the conservatism of this portion of the plant and have dis- 
couraged those who attempt to promulgate the law of recapitulation 
for the vegetable kingdom. The opinion of the probably majority of 
workers is expressed by Hill and de Fraine in the following quota- 
tion (i, p. 264) : "For these reasons we see no necessity for preserving 
seedling anatomy from the fate already meted out to other structural 
features, e. g., secondary thickening, which were at one time considered 
as indicators of phylogeny, a conclusion arrived at, either entirely 
or in part, by others who have paid attention to the facts of seedling 
anatomy." 
These investigators have in general confined themselves to one 
or a few families and have studied the relative variability of the 
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