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A STUDY OF THE SPORANGIA AND GAMETOPHYTES 
OF SELAGINELLA APUS AND SELAGINELLA 
RUPESTRIS. 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 
XXXI 
FLORENCE MAy LYON. 
(WITH PLATES v-IX) 
SELAGINELLA APUS. 
Sporancium.— It is by no means an easy matter to determine 
the origin of the sporangium in S. apus. It is quite possible, 
from a number of slides, to select a series which shal] seem to 
prove that the archesporium consists of two superficial cells 
originating just above the axil of a sporophyll (figs. 3, 4). It 
is equally easy to procure evidence that a single epidermal cell 
initiates the sporangium (figs. 7, 2, 5). This single cell may be 
either upon the sporophyll or removed by several intervening 
cells from its base. The exact line of demarcation between 
sporophyll and axis is indeterminate. The difficulty lies in the 
fact that until the sporangium is well established, consisting of 
some half dozen or more cells, there are almost no indications 
in the structure, or size, or staining qualities of these cells to 
distinguish them from the vegetative tissue. Moreover, a sporo- 
phyll originates in close proximity to a sporangium (fg. 5), 
and at about the same time and until it has established an 
apical cell there is no way of distinguishing it from a young 
sporangium. These facts render cross and tangential sections 
well nigh useless for an interpretation of the earliest stages. 
From serial radial, 7. ¢., vertical, sections of the strobilus, if cut 
with due reference to the phyllotaxy, it is possible to form con- 
clusions by comparison of the series of sporangia and sporo- 
phylls in the same rank and of different ages that appear in an 
exact median section. It is evident that the number of such 
124 [AUGUST 
