582 Benson.—Mazocarpon or the Structural Sigillariostrobus. 
through a megasporange and thus exhibits the total number of spores in the 
sporange, with Kidston’s drawings (reproduced in Scott’s Studies, Fig. 96 B), 
the resemblance is obvious. 
It must of course be borne in mind that one is dealing with thin slices 
of spores in Mazocarpon , but with their compressed entire body in Kidston’s 
material. 
The dimensions of the sporangia correspond. Text-fig. 2 shows eight 
spores, and this number is that suggested in Sigillariostrobus ciliatus. The 
size and surface markings of the spores correspond and, so far as sections 
can be compared with solid bodies, the form is surprisingly similar. In 
certain cases it can be seen they are distributed peripherally as is shown in 
Mazocarpon , Fig. 18, but there is of course in an incrustation no indication 
of the actual tissue, of the pad, though spaces occur between the spores. 
The spores in .S', ciliatus were thought to owe their irregular form to dis¬ 
tortion under pressure, and were regarded by Dr. Kidston as probably 
normally spherical. This interpretation was natural, as some of the bodies 
show a circular outline. It has been shown, however, in the description of 
the Mazocarpon megaspore that in several cases when a spore is cut 
tangentially the outline is circular (see Fig. 9). The spores of the French 
species described by Zeiller appeared to him to be derived from forms 
c a peu pres spheriques ’, although he added in a communication he kindly 
sent me on the subject (May 4, 1914), ‘ On ne peut, sur des spores aplaties 
comme on les observe presque toujours, juger avec certitude de la forme 
primitive \ In Mazocarpon the somewhat flattened form is the ‘ forme 
primitive ’. 
It is of course not impossible that some species of Sigillaria retained 
the ancestral form of the megaspore, for the Mazocarpon forms described in 
this paper are undoubtedly due to the germination of the spores while still 
in the sporange, and we are perhaps hardly justified in calling the body 
a mere spore. 
In Lepidocarpon there is evidence that the original form of the spore 
was tetrahedral, but, with the abortion of three members of the tetrad and 
the germination in situ of the* fourth, the whole sporange lumen was 
eventually occupied. Mazocarpon is exactly intermediate between Lepido - 
strohus and Lepidocarpon . It allots but one-eighth of the available space to 
each prothallus, and as these, when mature, are surrounded by a rigid spore- 
wall with characteristic appendages we incline to call them £ spores ’. 
If it should be shown that distantly allied species retained the tetra¬ 
hedral form of the spore it is probable that the number per sporange would 
be greater, as they would then not have had the space to extend much 
beyond the normal limit in Lepidostrobus . 
The spores in Zeiller’s 1 restoration of Sigillariostrobus Tieghemii in his 
1 Zeiller, loc cit., Fig. 4. 
