MEL AM PSORA. 



365 



particularly in a damp and cold spring, and may prove ver}- 

 destructive if it appears for several years in succession. The 

 mycelium evidently perennates in pine-shoots, and produces 

 new Caco7na-]intehes year after year till death of the host results. 

 It grows iutercellularly 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. 



Q 



I; 





Fio. 197. — C'tuoma pinitonjuum. Portion of CVooni'i-patch (enlarged). /', Cortical 

 cells partially absorbed or mncli compressed ; 0, ba.sidi:i from which spores (<■) are 

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

 membranous Lamellae, which disappear on formation of the spore-coats (</). 

 (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 develoj) 

 later in the 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 



