MELAM PSORA. 



365 



particularly in a damp and cold spring, and may prove very 

 destructive if it appears for several years in succession. The 

 mycelium evidently perennates in pine-shoots, and produces 

 new Caeoma-patches year after year till death of the host results. 

 It grows intercellularly especially in the rind parenchyma, but 

 also in the medullary rays of wood and bast; the contents 

 of the host-cells are absorbed by means of short lateral haustoria. 





Fig. 197. — Caeonia pinitwquum. Portion of Ctteoma-patch (enlarged). /, Cortical 

 cells partially absorbed or muck compressed ; 6, baaidia from which spores (c) are 

 abjointed in succession : the younger with delicate walls and separated by 

 membranous lamellae, which disappear on formation of the spore-coats (d). 

 (After R. Hartig.) 



The pycnidia are produced at end of May or beginning of 

 June, between the epidermal cell-wall and the cuticle of green 

 twigs ; before breaking out they may be observed externally 

 as light patches on the shoot. The Caeoma-patches develop 

 later in bhe second or third layer of the rind-parenchyma 

 (Fig. 196). In each patch the spores are produced serially from 

 short stalks to the number of twenty or thereabout, and ultimately 

 escape about June, when the cells of the parenchyma and 

 epidermis are ruptured. At first the spores are connected 

 together by intermediate cells which are afterwards absorbed 

 (Fig. 197). The mature spores are globose, oval, or polygonal 



