22 Mitchell.—Contributions towards a Knowledge of the 
of the vegetative leaves immediately following the tip of the cone, illustrating 
the gradual transition between the purely sterile and entirely fertile regions. 
c. In 5 . erythropus a second cone was produced on a fertile branch 
after an intervening sterile region, entirely devoid of any vestiges of 
sporangia ; in other words, two definitely fertile regions occurred on the 
same branch. 
This alternation of sterile and fertile zones in the four species quoted 
suggests the condition normally occurring in the more primitive Lyco- 
podiaceae. 
d. Fig. ii, PI. IV, represents an abnormal cone of oregana . 
That this is one branched strobilus, and not two cones, is demonstrated by 
the character of the leaves, and the distribution of sterile and fertile regions. 
The intervening leaves in the sterile regions retain, however, the external 
form of sporophylls. 
Distribution of the Sporangia on the Cone. 
Both mega- and microsporangia occur as a general rule on the same 
cone, and arise from the axis, onfe in the axil of each leaf. The disposition 
of these on the cone is not constant for the genus, there being four chief 
types of arrangement. 
A. One large basal megasporangium subtended by a specially large 
leaf, e. g. A. Kraussiana , A. Lyallii , A. convoluta , A. Bakeriana , A. sulcata , 
A. Galeotti , *S. rubella , A. Wildenowii , &c. 
B. Several basal megasporangia followed apically by microsporangia, 
e. g. S', spinosa , S. Vogelii , S. molliceps , S. helvetica , S. Braunii , S. oregana , 
S. rupestris , &c. 
C. Cones wholly megasporangiate or microsporangiate, e. g. S. atro - 
viridis , S. maequalifolia, S. gracilis, S. Lobbii, S . viridangida, &c. 
D. Indiscriminate arrangement of mega- and microsporangia, e. g. 
S. Martensii, S. haematodes , S. caulescens , S.patula , S. serpens, S.involvens , 
S. cuspidata , S. erythropus, S. flabellata, S . Wallichii, S. viticulosa, &c. 
Occasionally, exceptions from this rule are found; for example, 
(#) S. molliceps and S. viticulosa sometimes produce cones which are mega¬ 
sporangiate only, and (£) S. erythropus and S. flabellata entirely micro¬ 
sporangiate ones. This is not very surprising since, normally, the number 
of megasporangia in (a) and microsporangia in ( b ) greatly predominates. 
A detailed examination of the cones with special reference to the 
distribution of the sporangia leads to the following generalizations :— 
i. The megasporangia usually occupy the basal region. 
1 . The species which have acquired a definite arrangement (notably 
groups A and B) are those which show the greatest difference in shape and 
size between the micro- and megasporangia and the greatest elaboration of 
structure of the latter. 
