BeiereR ARTICLES, 
PRECURSORY LEAF SERRATIONS OF ULMUS. 
(WITH TWO FIGURES) 
Ir is a commonly accepted fact that embryonic plant tissue is mostly 
devoid of intercellular air spaces, and that gas interchange is accomplished 
from cell to cell by means of water which contains the necessary gases in 
solution. Such tissues are generally small in bulk, so that the most deeply 
lying cells are not widely distant from the outside atmosphere. Inter- 
cellular air spaces develop as the embryonic tissue 
increases in size, until at maturity an intricate system 
of passages, connecting with the atmosphere through 
stomata, insures proper aeration. 
Leaves in which air spaces are prominently 
developed to assist the process of photosynthesis form 
no exception to the rule. Tissues of young leaves 
) are compact, and form air passages during their 
growth after emergence from the bud scales. While 
wide observation is perhaps lacking to support the 
{view that the air spaces arise uniformly over the entre 
leaf, it is generally accepted as true. 
Racrgporski! has shown, hawever, that the leaves 
of certain lianas have a part which develops air space 
and stomata and hence becomes functional in advance 
of the main portion of the leaf. Such an organ he 
calls a Vorléujerspitze, and it consists of a slender, 
Fic. 1—Young pointed prolongation of the blade, from which aa 
leaf of Ulmus alata; partially separated by a slight constriction. 
thoseinwhichspongy *PPears that the purpose of the organ is to fig 
parenchyma has de- Process of photosynthesis as early as possi, main 
veloped. would help to accelerate the development of the 
portion of the leaf. 
While no such well-differentiated leaf organ is reported ee 
living in temperate latitudes, it seems certain that spongy parenchym® tion 
not always develop simultaneously over all parts of the leaf. An excep 
* Ractgorsk1, M., Ueber die V orliuferspitze. Flora 87:1-37- 19° 
224 
from plants 
[SEPTEMBER 
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