186 
completely surrounding the leaf is seen, and if a section be cut — 
near the apex, the chlorophyll is found to reach completely to the — 
bundle, which is not the case farther down. The guard cells of — 
the stomata are slightly sunken and, when viewed from above, are 
together somewhat ellipsoidal in shape. | 
The rounded succulent leaves with slightly depressed stomata — 
and waxy bloom are well adapted to withstand the hot suns which . 
beat in summer on the bare exposed ledges of serpentine in Ches- — 
ter county, Pennsylvania. Of Zalinum humile, confertiflorum, 
Greenmanii, napiforme, spinescens with terete leaves, the same thing — 
may be said. Inthe flat-ieaved Portulacaceae, although the leaves — 
are somewhat fleshy, the same adaptation is not so clearly marked. 
A repetition of the observation made above on Tahnum patens — 
needs to be repeated at this point. I found this plant growing on 
a rocky hillside with a southern exposure called Cerrode Guada-— 
lupe in the Valley of Mexico. The leaves in the hot sun of mid- | 
day were found more or less inrolled, thus giving to the plant a 
remarkably curled appearance. I have no doubt, although my — 
observations did not extend long enough to fully justify the con-_ 
clusion reached that, as in other plants, the leaves were inrolled as — 
a protective adaptation. An observation of Mr. Meehan, on the 
night closing of the leaves of purslane, shows that such motions — 
do occur in the Portulacaceae. Mr. Meehan notes* (Proc. Phila. 
Acad. Nat. Sci.) that in the list of plants having diurnal or noc-— 
turnal motion Portulaca oleracea does not appear. “ At sundown 
the leaves at other times at right angles with the stem rise and 
press the upper surface against it. The morning ex: ansion be- 
gins with dawn, and soon after sunrise the leaves are fully ex. 
panded. Mr. Isaac Burk has observed the same thing, not only 
in Portulaca but also in an allied plant of the West Indies, Za/inum 
patens.” The last observation of Mr. Burk shows that in 7. : 
patens the motion of the leaves is effected either by the approach > 
of night, or by too great illumination and heat. These facts are 
in line with the behavior of other plants, notably certain sensitive 
Leguminosae. Vilmorin says of this plant that «It keeps fresh 
in spite of heat and drouth, and will grow vigorously on unshaded . 
rocks.’’+ | : 
*1882. Meehan, Bull. Torr, Club, 9: 153. 
+ Les Fleurs de pleine Terre, 1124. 
