CONSERVATISM AND VARIABILITY IN SEEDLING OF DICOTYLEDONS 121 
seedling and the mature portions of the plant, looking to the former 
to provide clues for specific or generic relationship. The present 
paper records an examination of seedling structure over a wide range 
of families and orders in the dicotyledons, with a view to determining, 
on the basis of this comparative study, whether the anatomy of the 
seedling is variable everywhere, or whether it exhibits any characters 
which are sufhciently constant to be of value in marking out broad 
lines of relationship. 
The seedHngs of over 250 species belonging to 86 families were 
examined. External characters were observed and recorded and 
internal structure was studied by means of serial sections. 
Observations 
The observations of others as to the high degree of variability of 
certain characters, particularly the number of protoxylem clusters 
and the level of transition, were confirmed and their uselessness for 
classification emphasized. Another line of inquiry, however, was 
Fig. I. Thespesia populnea (Malvaceae). Serial sections from root to coty- 
ledon, a, root; b-d, hypocotyl; e, node (bundles of epicotyl in central ring); f-g, 
petiole of cotyledon; h, base of cotyledonary blade. (Xylem black, phloem white.) 
