108 
J. C. Th. Uphof. 
especially the future thick-walled outer cortex, at a later age only 
the thin-walled inner cortex contains living protoplasm with a few 
chloroplasts. At first, when very young, these cortical cells 
contain small intercellular spaces, but these soon disappear. The 
vascular bundle, which is in all species simple, contains a well 
developed phloem; the cells of the pericycle are relatively large, 
the cells of the protophloem, sieve tubes and phloem parenchyma 
are smaller. The vessels of the protoxylem and metaxylem are 
considerably narrower than those of the hygrophytic forms, owing 
to the reduced water supply of the plants. 
The cross section of a leaf (Fig. Ill, 7, V, 1, 7), is somewhat 
boat-shaped, the epidermis is thick-walled, covered by a thick cuticle. 
The wings of the leaf contain a thick sclerotic tissue, composed of 
two, sometimes of four, layers. The mesophyll is everywhere 
surrounded by the thick cells mentioned above; the air-spaces 
between the cells are small, except where stomata occur in the 
groove along the midrib of the aligular surface, and here the air¬ 
spaces become much larger. The stomata are protected by a very 
thick cuticle (Fig. Ill, 3), which contains opposite the entrance of 
each stomata, a small air chamber, leading through a narrower 
passage to the guard cells. 
The contrast in development of tissues between plants from 
very dry and exposed situations, and individuals of the same species 
from a moist and shaded greenhouse at Kew is striking (Fig. Ill, 
1-10). The adaptation of such xerophytic forms to a pure 
hygrophytic environment manifests itself at once. Plants from the 
latter possess almost horizontally placed leaves, instead of vertical 
ones (Fig. Ill, 5, 10). The leaf surface does not reflect the light: 
the awn at the apex of the leaf is considerably shorter in com¬ 
parison with that of the desert type (Fig. Ill, 4, 9); it has entirely 
lost its purpose, although it is composed of sclerotic elongated cells. 
The sporophylls, which form a four-sided spike, lie closer against 
the axis of plants from dry environments, protecting the mega-and 
microsporangia, than is the case with the sporophylls developed 
in a moist environment. 
A cross section of the stem (Fig. Ill), of the same age, shows 
a thinner cuticle ; the cell cavities of the epidermis and of the 
hypodermis are larger, because the cell-walls are thinner. All the 
walls of the cortex are considerably thinner, and the cortical cells 
possess living protoplasm with 4 to 5 chloroplasts. An important 
feature of the vascular bundle is the greater width of the vessels in 
