Notes. 
279 
subtends only a single sporangium. An exception has come at last, 
on a specimen of Lycopodium rigidum, Gmel., in the Glasgow 
University Herbarium; the sheet is labelled, Columbia, Hartweg, 
No. 1463. 
The specimen shows no special peculiarities beyond that to be 
described; the other sporophylls and sporangia are ot the normal 
type, even those in the immediate neighbourhood of the abnormality. 
Fig. 18. 
A single sporophyll, however, of slightly greater width than the 
average, subtends not one but two sporangia of slightly unequal size 
placed side by side (Fig. 18) : they are individually smaller than the 
average sporangia in th§ near neighbourhood on the same axis. 
The interest of this fact lies in its rarity : there is perhaps no 
character which marks off the plants of Lycopodinous affinity from 
others so clearly as the constancy of the solitary sporangium. Inter- 
polation of accessory sporangia, which is in some groups, such as the 
Ferns, so frequent a source of increase in their number, is entirely 
absent in the Lycopods. In the Psilotaceae it is true that numerical 
constancy is not observed, and irregularity of number of sporangia 
is not infrequent both in Psilotum and Tmesipieris. But in these 
