The Determinative Action of Environic Factors Upon Neobeckia acquatica Greene. 273 
florescence. The conducting tract was strongly developed, but the 
supporting tissüe was weak. One or two layers of palissaded cells 
were found underneath the upper surfaces and the remainder of the 
chlorophyllose tissue was disposed in the form of spongy parenchyma 
with large intercellular spaces. The epidermal cells over the midribs 
and its branches were noticeably larger and had heavier walls than 
elsewhere. These aerial dissected leaves by reason of the arrangement 
of the dissues described are much more efficient transpiratory Organs 
than the terminal bract-like 
leaves of emersed stems as 
was evident seen by a com- 
parison of the structure of 
the two (Fig. 11). 
On May 19, 1904 the 
cultures made from the cut- 
tings of 1902 were turned 
out of the pots for exami- 
nation. The large number of 
lateral branches previously 
mentioned had acted as off- 
sets, from which new plants 
had arisen, but still connec¬ 
ted with the parent in such 
manner that dense clumps 
were formed. A compara- 
tive examination of these 
plants and others of the same 
age and derivation grown in 
the aquarium was made in 
the latter part of October. 
The normal aquatic spe- 
cimens in July showed a 
single main root not more 
than 2 mm in diameter and Fig ' 12 ' Thicke a n s ed a gr ° Wn 
10 cm in length with a very 
thin secondary branches. The crown consisting of the top of the root 
and a stem fused with it had sent off one or two branches. The 
terrestrially grown individuals of the same age consisted of a clump of 
thickened roots produced by numerous offsets and branches from the 
crowns. These thickened roots were in clumps and were 10 to 15 cm 
