220 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



Orgajiization of the stem. — The stem fundament represented 

 in FIGURE 1 8 is quite homogeneous, consisting of slender longi- 

 tudinal hyphae, nearly parallel, but more or less interwoven. The 

 tissue at the base, perhaps not strictly belonging to the stem 

 proper, but forming the foot, is somewhat more dense. As the 

 plants age the stems become slightly differentiated. The core of 

 the stem does not keep pace in growth with the rather thick 

 external cylindrical portion. As a result the stem becomes hollow. 

 This probably is partly due to a lesser growth of the center, but 

 perhaps is to be attributed chiefly to the rapid growth of the 

 exterior, thus producing a tension which tears the core apart, 

 first leaving it in a more or less shredded condition, until finally 

 it becomes hollow. Except for a thin external layer the hyphae 

 of the stem increase greatly in size, come to lie strictly parallel, 

 and the protoplasm in the stout cylindrical cells becomes attenuate. 

 A thin external layer is made up of more slender cells rich in 

 protoplasm. This layer stains more deeply and is well shown in 

 FIGURES 26, 27, 29, and 32. The parallel hyphae of the stem 

 continue up to the junction of the stem and pileus. Near the 

 apex of the stem the cells become shorter, but arc still parallel. 

 The transition to the pileus trama is rather abrupt, shown by 

 the looser texture of the pileus trama and the strongly interwoven 

 hyphae. The hyphae in the periphery of the stem apex curve 

 rather abruptly into the lower surface of the pileus trama adjacent 

 to the hymenophore, a thin zone of which has a denser texture 

 than the main part of the pileus trama. 



The hlematogen. — The blematogen consists of a rather thick 

 zone of radiating hyphae, quite distinct from an early stage. 

 When the pileus fundament is first organized the limits between 

 pileus and the blematogen layer are very indefinite. But as the 

 hymenophore and pileus margin are organized the limits are more 

 clearly discerned. Later as the surface of the pileus becomes 

 better outlined the limits between blematogen and pileus are 

 quite clear. The cells of the blematogen layer become very large 

 and globose or subglobose. The hyphae become strongly con- 

 stricted at the septa, and very likely the middle lamellae become 

 weakened so that the cells readily separate. These loose cells 

 form the "powder" or "meal," which makes so conspicuous a 

 covering on the pileus and stem. The blematogen therefore 



