302 FIRST FORMS OF VEGETATION. 
finite expansion, determined only by the amount 
of pabulum which the decaying substances on 
which they are produced afford. The limits of 
some species are strictly marked out, and they 
rarely exceed them, retaining nearly the same di- 
mensions throughout their whole lives. It is prin- 
cipally the smallest and simplest species which 
are thus circumscribed ; and these make up by 
their immense profusion for the insignificance of 
their individual state. The largest and most 
highly developed species, which are but sparingly 
produced, frequently attain to almost fabulous di- 
mensions in favourable circumstances. The scaly 
polyporus (Polyporus squamosus), one of the com- 
monest fungi, everywhere to be met with on the 
decayed trunks of trees, especially the ash, and 
easily recognised by its brown scaly pileus, and 
white porous under-side, grows to a larger size 
than any other species. Instances have been re- 
corded of its measuring seven feet five inches in 
circumference, and weighing thirty-four pounds 
avoirdupois, having attained these vast dimen- 
sions in the short space of three weeks. The liver 
fungus (Fistulina hepatica) has been found on an 
ash-pollard weighing nearly thirty pounds. Dr. 
Badham, in his interesting work on the Zsculent 
Fungi of Britain, mentions having seen a fungus 
in the neighbourhood of Tunbridge Wells which 
