ST. ALBANS AND ITS NEIGHBOURHOOD. 
231 
be detected by the sense of smell before it is seen. Bricket 
Wood has also furnished one species of Irpex. Specimens of 
this may usually be found on the under side of fallen branches 
which are in an advanced stage of decay, and in such situations 
they furnish acceptable feeding-grounds for the plasmodia of 
several species of Badhamia. 
Mycetozoa.— The plasmodia above referred to are characteristic 
of the whole Class of the Mycetozoa, which, although usually 
grouped with the Fungi, are sharply differentiated from them by 
the existence of this, the motile stage of their metamorphoses. 
The individual sporangia are diminutive in size, but when 
growing in clusters are sufficiently conspicuous, as are also the 
sethalioid forms. 
There are 66 well-defined species recorded for the county, of 
which at least one-half have been observed in the district under 
consideration. 
Of the Exosporese, Ceratiomyxa mucida has been found at 
Harpenden. This is the only genus and species recognized in 
this section. 
The Endosporse include numerous Orders and genera. Of the 
genus Badhamia the species B. utricularis is the most frequent, 
and in favourable seasons may be observed in any moist wood¬ 
land, especially on retentive soils. Of the 14 species of Physarum 
recorded for the county at least 7 can be credited to this district; 
of these the most frequent are P. nutans, P. compressum, and 
P. vernum. In the neighbourhood of Harpenden Craterium 
pedunculatum and Dictydium umbilicatum have been observed, 
and at Wheathampstead Physarum diderma, JDidymium clavus, 
and Perichoena depressa . Bricket Wood has furnished four 
species of Trichia, all of which are widely distributed forms. 
The record for T. persimilis includes also T. abrujpta (‘ Trans.,’ 
Yol. Y), which differs from the type in the obtuse termination 
of the elaters, which end in diverging spines, a character some¬ 
times present in other species ; the spores are identical in both 
forms. At London Colney Perichoena variabilis, a very local 
species, has been found, and at Bedbourn Stemonitis fusca, 
a more common form, has been observed. Amongst the 
generally distributed species may be mentioned Didymium 
effusum, D. difforme, D. nigrijpes, Arcyria incarnata, and 
A. jpunicea. 
Most of these and other ubiquitous forms would in favourable 
seasons be found in almost any moist woodland which is not 
subjected to the inroads of the general public. An undisturbed 
environment is essential to their effective development. Heaps 
of decayed leaves and of straw have yielded to the writer several 
interesting forms, such as Physarum vernum, P. cinereum, and 
Sjpumaria alba. In such situations one may observe occasionally 
masses of plasmodium streaming over the decayed vegetation— 
white if of Didymium, grey if of Physarum, yellow if of 
Craterium. These and others have been found within a few 
