454 
BOTANICAL GAZETTE [DECEMBER 
the sun, but each leaf of the former class was about twice as large as one 
of the latter. 
Like those of a good many other Leguminosae, the leaves of this Medi- 
cago take a paraheliotropic position (fig. 3) during the hours when they 
are exposed to bright sunlight. This is identical with the nocturnal posi- 
Fic 3.—M. arborea, 
mesophytic form grown 
in full sunlight; leaflets 
in paraheliotropic posi- 
ion. X32. 
summer, and many of their branches die to the ground. The Artemisias _ 
tion. The movements of the leaflets are so slug- 
gish that it is difficult to ascertain definitely the 
percentage of illumination necessary to induce the 
position. As already stated, the leaves take this 
attitude permanently for some time before they are 
shed for the summer. 
Of the other woody non-succulent plants under 
discussion, the Matthiola alone at the end of the 
dry season has suffered no material injury. It is 
difficult to see how this plant, with its not incon- 
siderable rate of transpiration and its leaves des- 
titute of unusual epidermal protection and with 
loose, soft mesophyll, maintains itself so success- 
fully during the Mediterranean summer. Its most 
xerophytic characteristic is the manner in which 
the leaves are folded together upward along the 
midrib. 
The Helichrysum has a decidedly xerophytic 
aspect. Its cylindrical looking linear leaves are 
30-7o™™ Jong and usually only 1.4-1.5™™ wide; 
sometimes 3™™ wide. Both surfaces, but especially 
the lower, are covered with an abundant coating 
of felted, cobwebby hairs, and in leaves of the 
narrower type the spaces between the midrib and 
the recurved leaf margins are quite filled with a 
mass of hair. But this apparent provision against 
excessive transpiration, as already shown, does 
not prevent rapid loss of water, and indeed the 
poorly developed epidermis and loosely packed cells 
of the mesophyll are ill adapted to retain water. 
Helichrysum and Inula both lose more than half 
of their foliage by drying up before the end of the 
also lose by drying in situ sometimes more than two-thirds of their leaves, 
but the branches generally remain alive. 
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