462 BOTANICAL GAZETTE [JUNE 
ments of fourteen species found only on the seashore or in the adjoin- 
ing salt marshes showed that most of them possess thick leaves, while 
several cases merit the term succulent, ¢. g., Arenaria peploides (thick- 
ness 3™"); in this plant and several others the stem also partakes of the 
fleshy character. 
This increase in thickness of the leaf is always due, at least in 
part, to an increase in thickness of the palisade layer; for example, in 
Xanthium canadense and Atriplex hastata the palisade is about twice as 
thick in the maritime form as in the inland form. 
some cases the number of palisade layers is increased in the 
maritime situation; for instance, Convolvulus sepium has two layers in 
the inland form, but three in the maritime. 
4. Several species, such as Afriplex hastata, Xanthium canadense, 
and Polygonum aviculare, show a tendency to the isolateral form on 
the seashore, while they are distinctly bifacial when growing inland. 
In Xanthium the cells of the spongy parenchyma adjoining the lower 
epidermis are irregular in the inland form, but in the maritime form 
are elongated in a direction at right angles to the surface, forming a 
true palisade, which is more lacunar, however, than that on the dorsal 
side of the leaf. The only plant which showed the isolateral structure 
in both habitats is Cakile; this showed merely an increase in the num- 
ber of layers of palisade cells in the maritime form. However, of the 
fourteen distinctly maritime plants mentioned above, only three showed 
the bifacial structure, viz., Zigusticum scoticum, Artemisia Stelleriana, 
and Sabéatia stellaris ; so that the isolateral structure seems to be typical 
of the maritime condition.’ 
5. A marked increase in compactness of the mesophyll was observed 
only in Convolvulus sepium ; several other species showed this character 
in a very slight degree. 
6. Turning to the epidermis, the outer wall was found to be from 
one and a half to two times as thick in the maritime form as in the 
inland form in Cakile americana, Lathyrus maritimus,and Atriplex has- 
tata, but did not exceed 7p in any of these cases. 
7. The surface was found to be rougher in the maritime form in 
the case of Huphorbia polygonifolia and Atriplex hastata. 
. A noteworthy observation is the presence of hairs in the mari- 
de toon of Lathyrus maritimus and Convolvulus sepium, while no 
hairs were found in the inland form. The Convolvulus material col- 
lected on an exposed gravelly shore at Woods Hole showed long stiff 
? WARMING, EuG., Halofyt-Studier 247. 
