Lady Isabel Browne. 
153 
(c.) The only two species of Spencerites with which we are 
acquainted come from the Lower Coal Measures. 
The principal objection to regarding Spencerites as the cone of 
a primitive member of the order, is that the evidence that it 
belonged to one of the Lepidodendraceae is very weak. It seems 
clear that Spencerites was eligulate, and the presence of a ligule is 
characteristic of the leaves of all Lepidodendraceae, with the 
possible exception of the doubtful Archaeosigillaria ; it is also found 
in connection with the sporophylls of the better known forms ; it 
has not yet been detected in Sigillariostrobus, though its presence 
there will probably be demonstrated, for it has recently been shown 
that the leaves of Sigillaria were provided with a ligule (1). 
Therefore the absence of a ligule in Spencerites, coupled with the 
distal insertion of the sporangium and other less important 
differences, seems to show that though this genus is presumably 
the cone of a fossil member of the Lycopodiales, it is probably not 
Lepidodendraceous. On the other hand the spherical form and 
distal insertion of the sporangium may well be primitive, and it 
might belong to some ancient eligulate type (such as Archaeosigillaria) 
closely allied to the Lepidodendraceae. 
Heterospory is presumably always evolved from homospory, and 
the question thus arises whether this occurred in the case of the 
Lepidodendraceae within the order, or whether the common 
ancestor of the order was already heterosporous. Well-marked 
heterospory has been found in all investigated species of Sigillario¬ 
strobus (except in the doubtful 5. Crepini in which the spores are 
not known). Many species of Lepidostrobus, and all species of 
Lepidocarpon (to be considered presently) were heterosporous. 
The possibility of dicecism renders it almost impossible to be sure 
that any species is homosporous. Dr. Scott has recently asserted 
that it is almost certain that all Lepidostrobi were heterosporous, 
the two kinds of sporangia being borne on the same or on different 
cones (17). Dr. Scott thus maintains the heterospory of all 
Lepidrostrobi, without calling in the help of dioecism. Only one 
kind of spore is known in Spencerites, but we possess so few 
examples of this genus that the presumption of homospory thus 
afforded is weak. 
Still the attachment and form of the sporangium are suffi¬ 
ciently characteristic to enable us to distinguish the cones of this 
