118 MICROSCOPIC FUNGI. 



extremity (rarely frora tlie base) of tlie prismatic 

 spores. These tubes are straight or twisted, simple 

 or forked,, and each of them becomes divided by 

 tranverse septa into four unequal cells towards their 

 apex, from each of which is produced a spicule 

 bearing a sporidium, or spherical secondary fruit,. 

 in the same manner as in the genera Piiccinia and 

 Aregma. It should be observed, that the winter 

 spores of this rust are borne on the opposite sur- 

 face of the leaves to the summer spores : for whilst 

 the latter are developed from the under surface, the 

 former are found on the upper. This being also an 

 instance of di-morphism, the summer condition, 

 when spherical spores are produced, should not be 

 regarded as a distinct plant, and the name of 

 Lecythea cajprearum does not merit retention in the 

 list of fungi. 



There are five species of this interesting group,, 

 or genus, found in Great Britain, to the residue of 

 which we may only briefly allude. It has already 

 been stated that, in summer, the yellow spores of a 

 rust are found on the under surface of 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 TJredo hetulina of old 

 authors (begging their pardons, for some of them 

 still live), the Lecythea longica'psula of more recent 

 times,and the summersporesof lfe/a77?^sora hetulina^ 



