12 
DEVELOPMENT 
surface. In each there are primitive forms of sporophore, 
consisting only of a layer spread over the surface of the 
matrix, the spore-bearing surface covering this layer, and 
acking protection of any kind. (In some cases, however, 
as when growing on the under side of a log, a certain 
amount of protection is afforded by the habitat, and in 
others the presence of oxalate of lime is probably a safe¬ 
guard against attacks by slugs and insects.) From these 
simple forms the numerous complicated ones have been 
evolved. 
In one and the same species various types of hymenophore 
may occasionally be met with. The common Polystictus 
versicolor affords a very instructive example (see Plate I.). 
In this species the sporophore is completely adnate when 
developed on a broad horizontal substratum such as the 
under surface of a prostrate log (Plate I., 4). When 
growing from the vertical side of a trunk, however, it is 
adnate at first, but gradually becomes free at the upper¬ 
most margin, and grows away at right angles to the adnate 
part (Plate I., 5). (A wholly adnate sporophore on the 
under side of a log will soon develop a free edge if the log 
is rolled over to such an extent that the fungus is in a vertical 
position.) 
If the fungus develops on a small branch, each end of 
the free part has a tendency to grow towards the other 
(Plate I., 7). Sometimes its position— e.g. } on the upper 
surface of a log—allows the recurring ends to meet, and 
they unite, the result being an umbrella-shaped sporophore 
with a central stem. The upper part is sterile, and protects 
the hymenium, which occupies the lower surface, and some¬ 
times the stem also (Plate I., 8). 
Polystictus versicolor belongs to the family Polyporaceae, 
characterized by the hymenium consisting of closely-packed 
tubes. This family is the most highly specialized of all 
Basidiomycetes. The tubes afford an enormous spore- 
