INJURIES INDUCED BY PLANTS 



167 



season when the apex of the green leaf- fascicles on the young 

 shoots is projecting somewhat from the leaf-sheath, pale yellow 

 patches f to li inch long and -J- to f inch broad appear upon the 

 green cortical tissues of the shoots (Fig. 97), and on these, with 

 the help of a pocket lens, numerous small rather deeper yellow 

 tubercles, the spermogonia, may be made out. These are 

 formed partly in the epidermal cells, and partly between them 

 and the cuticle, the latter being raised up to cover the spermo- 

 gonium (Fig. 98). The ><?;/ztf-layer originates in the second 

 or third row of cortical cells, and is formed by the inter- 

 cellular mycelium growing outwards from the interior of the 

 stem to produce a sporophore in that 

 region. The secidiospores are afterwards 

 distributed by abscission from the apex 

 of basidia in the usual way. While the 

 formation of this internal sporogenous 



FIG. 97. Apex cf a young 

 pine-shoot showing the 

 sporogenous layers of 

 C . pinitorquum through 

 the ruptured cortex. 

 Natural size. 



FIG. 98. Transverse section of a sporogenous layer 

 of C. pinitorquum before the cortex has ruptured. 

 Two tubercular spermogonia are visible in the 

 epidermis. 



layer is proceeding, the surface of the part of the cortex affected 

 is constantly assuming a deeper golden yellow colour, while* 

 at the same time, it forms a cushion-like elevation which 

 results in the development of a longitudinal fissure (Fig. 97) in 

 the external layers of the cortex through which the spores are 

 shed. The tissues of the cortex beneath the sporophore after- 

 wards die as far in as the wood, and a callus is formed, under 

 favourable circumstances, in about a year. 



During the development of the spores, and for some time 

 afterwards, the young shoot continues to elongate normally, 

 except at the seat of the disease. The result is that the diseased 



