92 
Heterospory in Sphenophyllum Davvsoni. 
kind described for Calamostachys may have been going on in 
Sphenophyllum Dawsoni. 
The large size of the spores figured and the abortive spores 
accompanying them were noticed during the examination of a section 
in the Cambridge Botany School Collection. The slide in question 
was prepared by Mr. Lomax from a specimen obtained from Shore, 
Littleborough, Lancashire; it is an oblique tangential section of a 
strobilus of Sphenophyllum Dawsoni, which, judging from this and 
another more median section of the same specimen, was 15 mm. 
long by 8 mm. in diameter. The number of internodes preserved 
appears to be six, and this conclusion is supported by a comparison 
of the total length with the distance between two successive whorls 
(about 2-5 mm.); but towards the apex, which is represented in the 
more median section, there is some indefiniteness. 
In the lowest whorl but one in the section first mentioned a 
sporangium occurs (see Fig. 14) which contains fewer and larger 
spores (a. a.) than the adjacent sporangium, together with a number 
of abortive spores (b. b.) From a number of measurements of the 
diameters of the spores, the average in the sporangium in question 
is 106/x; the maximum diameter is 120/x, and several reach 115/x. 
Similar measurements in the adjacent sporangium figured give an 
average of 83/x, with a maximum of 90/x. The presence of the 
characteristic spines (c. c.) shows that the spores in both sporangia 
had reached maturity. 
The maximum diameter recorded by Williamson and Scott for 
spores of S. Dawsoni is 104/x. 1 
1 Loc. cit., p. 939. 
