436 BOTANICAL GAZETTE [JUNE 
more infrequent. In an epidermis a year old, seen from the surface, 
the boundaries of the original epidermal cells can usually be distin- » 
guished. They are somewhat thicker than the secondary transverse 
oad) < walls, which in turn are thicker than the secondary 
longitudinal walls (jig. 2). With the formation of 
es cork the epidermis is of course split longitudinally 
and soon begins to undergo disorganization. No 
trace of it is left in a tree 8°™ in diameter. 
Or The number of stomata produced varies greatly, 
L000 SEE 
but seems to be largely dependent upon external 
conditions. A rapidly growing tree, for example, in 
4 a moist locality has many stomata, while a slow- 
e growing tree in dry soil develops very few. The 
. 
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stomata are depressed and the epidermal cells bound- 
ing the guard cells are somewhat modified, being 
longer and narrower than their neighbors (fig. 3)- 
Fic. 2.—Surface Most of the stomata are transverse to the axis upon 
view of epidermal which they are borne, a few are oblique, but appar- 
ae nay Bag ently none of them occupy a longitudinal position. 
ain ie miei’ ary Lhis is doubtless to be explained by the fact that 
of the original cell, the stomata are formed late in the development of 
which has under- the epidermis, the wall separating the guard cells 
liad i representing one of the secondary transverse divisions 
of an epidermal cell. In the majority of 
cases the cells surrounding a stoma contain nie ‘ik 
anthocyan, so that to the naked eye the 
stomatal region looks like a minute red 
speck in the epidermis. This peculiarity _}{ \@/¢ $# 
affords a ready means for detecting the SS LE 
stomata. LY aa 
Epidermal hairs are developed on very ae 
young twigs before the primary tissues are Fic. 3.—Stoma_ with sur- 
fully differentiated. They are simple and TU"dins ie nana crcaals 
unicellular, with thickened walls, and scarcely cage 
extend below the cuticle (fig. 4). These hairs never persist through 
the first vegetative period, but dry up and fall away as soon as the 
cuticle begins to thicken. Their former position is often marked by 
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ay 4, 
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