332 BOTANICAL GAZETTE [MAY 
tapetal characters are notoriously variable. Such bearing as it 
has, however, is in harmony with what may be inferred from 
other features of the sporangium. It involves no disorganization 
of the cells, no multiplication of nuclei except as related to cell- 
division, and no mingling of naked protoplasm with the young 
spores. 
One of the facts which Vines advanced as an argument 
against the usually accepted classification of Isoetes is the 
absence of a strobilus, the characteristic arrangement of the 
sporophylls in the Lycopodiales. He contrasts also the elon- 
gated, slender, branched stem of Lycopodium or Selaginella with 
the short unbranched stem of Isoetes, which much more closely 
resembles that of some eusporangiate ferns. It may be doubted 
whether such superficial characters, unless accompanied by 
internal features of which they are the outward expression, have 
any value in settling the relationship of distinct genera oF families. 
At all events, their usefulness in angiosperm taxonomy is limited 
to the distinction of species; they would be of no use in decid- 
ing the family to which an undetermined species ought to belong. 
I am inclined to think the whole plant-body of Isoetes can best 
be explained as a shortened strobilus, just such as Lycopodium 
would become by suppression of the stem and axis, while allow- 
ing a normal development of the leaves and sporangia. 
The most obvious diagnostic character of the three groups 
of pteridophytes is furnished by the leaves. The leaves of the 
Isoetes are sui generis, and afford little ground for associating !t 
with any one group rather than another. Though they are rela- 
tively few and large, as is the case among ferns, thelr 
unbranched outlines and simple tissues show an analogy wit 
the leaves of Lycopodiales ; while their peculiar vascular bundles, 
and chambers, and diaphragms remove them as effectually ine 
either group. There is record, it is true, of a fossil Isoetes with 
a branched leaf, indicating, when taken in conjunction with the 
sudden reduction of the vascular bundle just above the ligule, 
the possibility that the present form of the leaf may be @ 
reduced one representing a more complex ancestral type- oy 
