INJURIES INDUCED BY PLANTS 



75 



the interior, g, which contain chlorophyll, do not succumb for 

 some time to the action of the mycelium, //, which here and 

 there effects an entrance. The depression at the entrance 



to the stomata, being lined with 

 waxy granules, prevents the en- 

 trance of any haustorium, i. The 

 dark brown perithecia (Fig. 22) 

 which ultimately arise on the 

 cushion are scarcely recognizable 

 with the naked eye. They are 



FlG. 22. Perithecium of T. para- 

 sitica. The dark brown sphere 

 shows a round aperture at its 

 apex, and bristle-like hairs 

 which project from its upper 

 half. A portion of the wall 

 has been removed from the 

 lower left-hand side in order to 

 show the pale contents, which 

 consists of asci and paraphyses. 

 These are shown more highly 

 magnified in the lower part of 

 the figure ; a representing rod- 

 like bodies which are often pre- 

 sent ; b, asci with spores, and 

 c, isolated spores. 



FlG. 23. Herpotrichia nigra on the 

 spruce ; half natural size. 



characterized by having bristle-like hairs distributed over the 

 upper half. In the interior of the perithecia are often to be found 

 small rod-like organs, a, besides the asci, b, which hold eight 

 grey spores, usually consisting of four chambers. Should these 

 spores succeed in obtaining a suitable footing on the branch 

 of a silver fir, they speedily germinate and produce the disease. 

 The mycelium spreads parasitically from the point of infection 



