220 The Relations between the Station of fApnl, 
iiip smaller diametei nf the 
former, in consequenc terrestrial form has, besides, 
central air-channel. not separated, as in 
stronger col enchymatised n^eUs,^ ^ e 
the aquatic form, y c ic more strongly developed, and 
closing the vascular un til t p e lumen disappears. 
the cells f re ^ more numerous, and contain three 
The vasculai bundles a aquatic form, 
times as many vessels a , bv t i. e circumstance that 
These differences aie expla i . tbe a aion of the 
the shoots of the land «X s Vem while the water- 
winds, require a firm mee a1 ^ ac ^ y ommodate themselves to 
sprouts must be light The greater part of their 
every movement of the wat . g so i id elements are 
volume is taken up > y P agri ’ al shoots , producing more 
almost entirely wa "^? g * isting in a drier atmosphere, eva- 
numerous leaves an • , g aquatic shoots, and 
porateto a greater extent than d0 ^ or the conduction 
hence in the former find the syster n ^ ^ Eva- 
of water more strong y P g furtber diminished by the 
circumstance that “the Lrk is only slightly developed, and 
that the air-spaces are ms.gmflcant. oriai - n order to 
We see, further, tha adapting themselves to 
avoid temporary submergen ^. e y provided wit h a long, but 
the movements of the > The stem of the aerial 
thin and permanently flexible ste . lh the thick- 
leaves is six times shot el, ^ 01 ^ y trengthened by a 
ness. 1 hey are ur ^eel f rom t he midrib of the leaf, 
tissue which projects 1 t he shade, assimilation is 
As the aquatic leaves aie no chlorophylhferous 
in them more “VroSrfy developed than in the 
parenchyma is m them mo ^ 1 t »^ ed again5t too intense 
aerial leaves, lh . hairs, pressed closely upon 
evaporation by numero f stom ata is approx- 
the surface of the leaf. The numn ^ a „ rial leaf th ey 
™ a ' c4flT a on‘tb' 0 tw° T »d in & tbe aquatic leaf on the 
UP ^ large epidermic cells whidt occur singly o^tlmupper 
side of the aerial leaf m th e sta tion. Their inner mem- 
adaptation to the dryness f co l n(j . t . on _ These cells readily 
brane is in a veiy y ded as reservoirs which in 
absorb water, and mus J t heir water and prevent the 
time of need give off a P , cells f rom withering, 
epidermis and the f ienc £ d between different 
Further comparisons aie next 
