RUSTS. 
335 
birch-leaves. These must be sought on the young twigs or 
suckers, proceeding from the stumps of trees which have been 
cut down ; pale discoloured spots on the upper surface of the 
leaves indicate the presence of the rust beneath. This is the 
JJreclo betulina of old authors (begging their pardons, for some 
of them still live), the Lecythea longicajosula of more recent 
times, and the summer spores of Melampsora betulina , according 
to M. Tulasne and his disciples. When fresh, it is reputed to 
exhale a faint odour, as of the primrose. During the winter 
and spring months the wedge-like spores of the second crop 
are matured on the fallen leaves (Plate XIII. figs. 20, 21), and 
these are capable of a speedy germination, and the production 
of secondary reproductive bodies, as in the willow rust above 
alluded to (Plate XIII. fig. 24). 
Probably, also, the similar rust on the poplar (Plate XIII. 
figs. 18, 19), or on the aspen, may be met with under like 
conditions ; i. e., the summer spores, which are yellow and 
spherical, on the living leaves, and the brown permanent 
masses of winter spores on the fallen and decaying leaves. 
The sole remaining British species is not uncommon on leaves 
of the common spurge in gardens ; and whilst the yellow pul- 
verulent spores occur on the upper, it will not be improbable 
that black permanent spots will be found on the lower leaves 
(Plate XIII. figs. 22,23), inclosing closely-packed, rudimentary, 
elongated or wedge-shaped cellules of the winter spores. 
In conclusion, I will offer a brief guide to the distinctive 
features of each of the several groups which have been noticed 
in the foregoing pages, for the assistance of those who may 
wish to pursue the study further than we have been permitted 
to carry them. 
Spores of one order — 
Simple and free. 
Without appendages. 
Inclosed in separate cells TIredo. 
Not inclosed Lecythea. 
With appendages. 
Deciduous Trichobasis. 
Permanent Uromyces. 
Concatenate. 
Afterwards free Cystopus. 
Compound Polycystis. 
Spores of two orders — 
Cylindrical, septate Coleosporium. 
Wedge-shaped, compact Melamysora. 
