ATKINSON— GALERULA IN NORTH AMERICA. 359 



of the cortex does not appear to be sufficiently clear, and does not 

 separate the true species of this section of Galerula from species of 

 Naucoria and Heheloma having a more or less pseudoparenchymatous 

 cortex. According to the principle followed in the present arrange- 

 m.ent, the cortex of the pileus in this section of the genus is more 

 highly differentiated than the simple pseudoparenchymatous cortex. 

 There is an outer layer clavate to pyriform cells, in the young stage 

 forming a more or less definite palisade layer. In age these cells 

 in certain species swell to a large size, as well as certain cells beneath 

 this layer, so that the cortex takes on a pseudoparenchymatous 

 aspect, but close examination shows the large pyriform cells of the 

 surface, and it can be seen that the pseudoparenchyma is of a dif- 

 ferent origin and structure from that which I have termed simple 

 pseudoparenchyma in certain species of Naucoria and Heheloma. 



Still further differentiation is manifest in the structure of the 

 lamellae. All species recognized here as belonging to Galerula are 

 provided with specialized cells in the hymenium, usually termed- 

 cystidia. These vary in form and in their distribution on the: 

 lamellae. They will not be discussed in detail at the present time- 

 In the synopsis of the species presented below their form and ar- 

 rangement is clearly indicated. The species with a corticated pileus 

 are regarded as more highly specialized, those of the last section 

 having reached the highest stage of specialization with corticated 

 pileus and lecythiform or stopper-shaped cystidia. This specializa- 

 tion is further indicated by the large number of species with two- 

 spored basidia. 



There appear to be rather clear evidences of progression in de- 

 velopment from the simpler forms of the species with a homogeneous 

 pileus, and diverging in two lines, one line culminating in the corti- 

 cated species, the other line retaining the homogeneous structure of 

 the pileus. Galerula angusticcps proves to be an interesting species 

 in this connection. Some individuals have the pileus homogeneous in 

 structure, while others show a rudimentary cortex of the Galerula 

 type. It is therefore placed in both of the principal groups in the 

 synopsis. After a critical study of the species in allied genera has 

 been made, it may be possible to make some suggestions concerning 

 the relationships within the group. 



