SPORE-PRODUCING MEMBERS 377 
in the middle of the internode (Fig. 202), and in Stachannularia ot 
Cingularia at the top of the internode (Fig. 204). Such facts as these, 
here only briefly sketched, must be taken into account in discussing the 
morphology of the strobilus of the Equisetales, and in deciding the true 
chararacter of the sporangiophores. But before this is entered upon their 
detailed structure and development must be examined. 
SPORE-PRODUCING MEMBERS. 
Naturally the development of the spore-producing members can only 
be followed in the living genus, though from the similarity of their mature 
features to those seen in the fossils it 
is probable that there was substantial 
similarity in these also. In Egutsetum 
the axis, which is about to produce 
a strobilus, ceases active growth in 
length, retaining a conical form: the 
sporangiophores arise upon it in acro- 
petal order, as convex swellings (Fig. 
205). The details show some varia- 
tion in different species: they are here 
described for Egudsetum arvense and 
limosum.1 In the first stages the spor- 
angiophores are not unlike the sterile 
leaf-sheaths, involving, as seen in 
longitudinal section, some six cells, 4 = 
which grow out with a fan-like tracery = ; 
and repeated anticlinal walls (Fig. } 
206 A). This similarity has been used 
as an argument favouring the view that Fic. 205. 
the sporangiophore and the bract-leaf __Half-developed strobilus of Zguisefum arvense, 
- in longitudinal section, taken at end of October. 
are results of ‘ metamorphosis” of  xs50. (After Hofmeister.) 
essentially the same part, a point 
which will be taken up later. Single superficial cells near the margins 
of the convex outgrowths are early recognisable as the parent cells which 
give rise to all the essential parts of the sporangia, though adjoining 
cells also grow out together with these to form the sporangial body: the 
origin of the sporangium is thus of the eusporangiate type (Fig. 206 a, B). 
At an early stage there is active growth in the middle region of the 
sporangiophore, which results in an inversion of the young sporangia, so 
that they come to point with their apices towards the axis. Each parent 
cell first divides periclinally (Fig. 206 a): the inner cell gives rise only 
to a portion of the sporogenous tissue, the outer undergoes further division, 
first by anticlinal, later by periclinal walls (Fig. 206 8, c, D) The inner 
1 Studies, i., p. 496, etc. 
