338 BOTANICAL GAZETTE [may 
embryo show the necessity of making it a separate family. The 
Lycopodiales so constituted comprise six genera pretty widely 
separated in morphological characters, as from the antiquity of 
the group one might naturally expect. But the extreme differ- 
ences are not greater than in the Filicales. If we can include 
Azolla, Marsilia, the common ferns, Hymenophyllum, the Marat- 
tiacee, and the Ophioglossacee in one group, it ought not to 
appear inconsistent to include Psilotum, Lycopodium, Phyl- 
loglossum, Selaginella, and Isoetes ina group of coordinate rank. 
A fuller knowledge of the three little-known genera may tend 
to confirm this view, especially if they depart as widely from 
the remaining genera in other characters as in general habit 
and sporangia; but if their gametophytes, spermatozoids, and 
embryos agree very nearly with Lycopodium and Selaginella, it 
will probably be better to make of Isoetes a fourth group of 
pteridophytes equivalent in rank to the three now universally 
recognized. If an affinity with seed plants must be sought, the 
evidence points to a connection with gymnosperms rather than 
with monocotyledons, 
SUMMARY. 
1. The stem apex lies at the bottom of a funnel-shaped 
depression, around the sides of which the leaves are arranged 
spirally. This depression is produced by the expansion of the 
cortical cells of the stem in all directions. 
2. The leaves arise as crescent-shaped bands of meristematic 
tissue. At first the basal part of the leaf (the sheath) grows 
most rapidly; afterwards the region of growth is transferred to 
the part above the ligule. There is no persistent or sharply- 
marked zone of meristem. The whole leaf is meristematic a 
first; it then gradually passes into permanent tissue, the change 
beginning at the apex and extending gradually downwards. 
3. The air-cavities are formed out of four longitudinal bands 
of cells, which after losing their contents and power of multipli- 
cation are ruptured into transverse partitions by the growth of 
the other parts of the leaf. The size, but not the number of the 
air-cavities, increases with the age and growth of the leaf. 
