Igo BOTANICAL GAZETTE [SEPTEMBER 
(d) color of twigs; energy absorption; protection; (e) indetermi- 
nate growth; maximum growing season; (/) food storage capacity; 
amyliferous tissue; (g) high vitality of lateral buds; (k) vegetative 
activity of shoots; quick response to warmth and light; rhizogény; 
(¢) medullary rays; marginal cells; extension into bark; (7) large 
and numerous pits in wood elements; (k) bark; thick, tough, 
elastic, persistent; (/) unobstructed conduction in roots; (m) great 
extent of root system; () large number of seeds; (0) anemophily; 
(p) extreme protection of embryo; thick, resistant seed coats; 
(q) food storage in embryo; (r) fruit long persistent on the tree. 
Summary and conclusions 
1. Negundo aceroides does not appear as an authentic species in 
the geological record before the Glacial Period. 
2. The fundamental Negundo characters made their appearance 
as early as the Upper Cretaceous, but only as minor variations from 
the Acer type. | 
3. In structure of leaf, efficiency of transporting tissue, capacity 
of storage organs, and in maximum utilization of light, heat, and 
growing season, Negundo became peculiarly adapted to the rigors 
of a glacial environment. 
4. The impetus acquired by Negundo during the strenuous period 
of its adaptation to glacial conditions is still manifest in the pro- 
nounced inconstancy of the Negundo type. However, there seems 
to be no true reversion to the pre-glacial ancestral forms. 
5. In practically every particular, except the morphology of 
the fruit, Negundo is now essentially different from the true maples. 
6. Upon purely anatomical grounds, it appears that Negundo 
possesses characteristics of generic rank, and while the box elder 
is undoubtedly a descendant from the ancestral Acer stock, it has 
now reached a stage of differential development that may fairly 
exclude it from the group of true maples. Thus there seems to be 
ample justification for the name ‘‘Negundo aceroides Moench. 
1794.” 
In conclusion, I wish to express my thanks to Professor F. H. 
KNowLTON for facts in regard to the geological record of the box 
