433 
made of parts midway between two well developed fibro-vascular 
bundles. 
In five species of Adiantum 1 found no palisade tissue. The 
cells of both upper and lower epidermis contain chlorophyl. The 
cells of the upper epidermis are irregular in shape toward their 
lower side, extending down into the mesophyl. The air spaces 
are relatively large and numerous. ‘The number of cells in thick- 
ness of the mesophyl is two. I examined six species of Dryopieris 
and found a palisade tissue of two layers of cells, sometimes 
arranged perpendicular to the epidermis. Both layers of the epi- 
dermis contain chlorophyl. The cells of the upper are sometimes 
irregular in shape, where the palisade tissue is not arranged with 
its longer axis perpendicular to the epidermis as in A. “ipéeron. 
The air spaces are very large, extending through a depth of two or 
even three cells, There are small air spaces all through the pali- 
sade tissue. The number of layers of cells of the mesophy] is five. 
In seven species of Nephrolepis the layers of palisade cells 
have their longer axes parallel to the epidermis. There is no 
chlorophyl in the epidermis except in WV. molle. There are a few 
small air spaces in the palisade layers, while the air spaces directly 
Over the stomata are not deeper than one cell, and in each case 
are covered by one long cell or the protrusions of two. The cells 
of the spongy parenchyma are about twice as long as the palisade 
cells and lie parallel to them. The number of layers in the meso- 
phyl is six, except WV. molle which has two, and JV. Phillipinensis, 
five. 
Three species of Polypodium have a palisade tissue of two 
layers of cells. There is no chlorophy] in the epidermis, almost 
No air spaces in the upper layers and very large spaces below, 
often extending to the upper layer. There is no sharp distinction 
between the upper and lower layers of cells in shape and size. 
The number of layers of cells in the mesophy] is four. 
In eight species of Pveris there is a palisade tissue of one 
layer, in P. Cretica of three layers. In four species chlorophy]l is 
Present in the epidermis, and in four there is no chlorophyl in the 
epidermis. The air spaces are very large and numerous. The 
Cells of the lower layers of the mesophyl are sinuous and very ir- = 
regular in shape and size. The number of layers of cells in the 
