476 



FUNGOUS DISEASES OF PLANTS 



With reference to the development of the sporophore, the early 

 studies of Hartig would indicate that it begins as an ovoidal or 

 spheroidal body, made up of closely united hyphae, the direction 

 of whose growth is soon mostly longitudinal. For some time there 

 is no differentiation of stem and cap, but after the hyphal mass has 

 attained a length of several millimeters, differentiation into these 

 parts becomes evident. In the first place, an annular furrow is 

 formed by cessation of growth in certain filaments near the apex, 

 and this annular furrow delimits pileus and stipe. Subsequently, 



Fig. 237. Armillaria mellea: Rhizomorphs and Young Sporophores 

 (Photograph by H. H. Whetzel) 



the outer layer of filaments from below and from above this fur- 

 row become interlaced, and thus is formed an early stage of the 

 veil, or membrane, inclosing the area in which the hymenium is 

 eventually produced. As growth proceeds, the overlapping periph- 

 eral elements become wholly indistinguishable, the pileus is then 

 developed by successions of epinastic and hyponastic growth, the 

 principal growth being in the direction of the pileus. The hyme- 

 nial surface is thereafter differentiated by the growth downward of 

 alternating radial hyphal bands, which form the trama, or middle 

 tissue of the lamella, bearing eventually the hymenium or surface 

 from which the basidia are produced. With the rapid growth in 



