W. C. Worsciell. 
i 64 
large, terminal sporangium. We may imagine, further, a sub¬ 
division of this latter into three parts, as in the male sporophyll of 
Welwitschia and if, of these three, we postulate two inferior and 
one superior sporangium, of which the former, during the continued 
process of sterilisation, became modified into two vegetative lobes, 
while the latter became further sub divided into two, three, four or, 
even more parts, we should obtain the type of sporophyll of the 
Psilotaceae. The primitive type in these plants may have been 
retained owing to their early adoption of a saprophytic habit; this 
seems more probable than the view that they represent a case of 
reduction. A similar stage to that of Psilotum and Tmesipteris is 
seen in Sphenophyllum majus , with 4-or 5-partite synangium 
and in 6'. trichoniatosum in which a single sporangium occurs in or 
near the axil of the sporophyll. The next stage in differentiation 
was that in which the sporophyll became still further forked, and 
the synangia correspondingly increased in number, as in some forms 
of Tmesipteris and in Cheirostrobus. Again, the synangium became 
raised up on a stalk from the top of which the one or two sporangia 
were pendulous, as in other forms of Tmesipteris and Spheno¬ 
phyllum. In S. Daivsoni there are two such sporangiophores to 
each “ bract.” This latter really represents the sterilised inferior 
sporangium or synangium and is here simple and unforked. The 
term “bract” is of merely descriptive value. In S. Romeri there 
are three whorls of sporangiophores ; each is more or less peltate, 
bearing two pendulous sporangia, and is fairly massive. A much 
greater elaboration of the structure of the sporangiophore is found 
in Cheirostrobus , which plant, although doubtless a very primitive 
type as a whole, has yet, as regards its sporophylls, become very 
highly differentiated and specialised ; the same remark applies, 
although in less degree, to Sphenophyllum. In Cheirostrobus each 
sporangiophore belonging to each lobe of the palmately-divided 
sporophyll is a perfectly peltate structure bearing 4 elongated 
sporangia. 
Before proceeding to mention the peculiarities of further 
types, I will pause here to consider the exact morphology of these 
various “ sporangiophores.” In some forms of Tmesipteris this 
structure is replaced by a leaflet perfectly resembling the normal 
leaflets or lobes of the sporophyll. Here we see an excellent 
and rare case of a vent rally- placed leaflet. It shews clearly, to 
my mind, that the sporangiophore of Tmesipteris is exactly homo¬ 
logous with such. But if so, then are the sporangiophores of 
