614 BRITTON: VEGETATION OF THE 
is correlated with a hydrophytic, and physiological dryness with a 
xerophytic vegetation.” * 
With this brief general survey of the subject we will now dis- 
cuss the ecological structure of some of the plants of the North 
Haven sand plains. 
A number of perennial plants, of which the milkweeds (As- 
clepias), Lespedesa, Baptisia tinctoria, Lupinus perennis, Cracca 
Virginiana and Meibomia are good examples, have long roots 
that go down deep into the subsoil and bring up moisture from 
a lower level to supply the needs of the plants. Clovers also do 
this and are often able to withstand drought and even make 
growth when other plants fail and perish. Asclepias Syriaca and 
A. amplexicaulis grow quite luxuriantly upon the sand and in no 
small measure must this be attributed to the deep growing roots 
and rhizomes, which are not only able to obtain water but may 
hold it for some time or until it can be used by the plant. (/7. 24, 
6, shows a colony of Asclepias Syriaca.) A. verticillata is not a 
deep-rooted plant, but the roots are fleshy and the leaves have a 
narrow form exposing much Jess surface than the broad-leaved 
species. The milky juice of these plants, while not thoroughly 
understood, seems to be correlated with other xerophytic charac- 
ters and probably prevents the escape of water. If the plant 
is cut or wounded the milky juice soon closes over the wound, 
forming an impervious rubber-like coating. On account of this 
substance many plants with a milky sap, like Lactuca, Asclepias 
and Euphorbia, will wilt when cut and placed in water, because 
the water cannot enter the stem through the coating formed by 
the milky juice. 
Some of the legumes in addition to their habit of deep-rooting, 
have the surface of stem and leaves well protected by hairs. 
Lespedeza Stuvei and Cracca Virginiana are good examples. 
A fleshy leaf has been considered the most perfect type of 
xerophytic adaptation, and this is found in Polygonella articulata 
and to some extent in Euphorbia polygonifolia. 
In Cypripedium acaule and certain liliaceous plants like Sa/e 
nia (Polygonatum) and Vagnera (Smilacina) there is some degre 
of fleshy development of the leaf and stem tissues. We find also 
Sa 
* Schimper, A. W., /. c. 4. 
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