INJURIES INDUCED BY PLANTS 175 



often die in a few years, after which the parasite frequently 

 spreads downwards from the base of the branch to the main 

 axis of the stem (Fig. 105). Even should the latter die the tree 

 will still remain alive, provided there are branches and twigs well 

 provided with leaves beneath the canker-spot. These branches 

 constitute a kind of new leader, and the dead crown forms 

 the " resin-top " or " resin-leader " (" bird-resin "), which was 

 regarded by Ratzeburg as the result of injury caused by the 

 Pine Beauty Moth, and designated as " spear-top." 



The disease has also been described by this observer as 

 " moth-wither," or, in other words, as the result of the attack of 

 Phycis abietella ( Tinea sylvestrella, Ratz). 



Three species of pine-blister-rust are to be distinguished in 

 the cortex of trees, viz. : 



(1) Peridermium Strobi, which occurs only in the cortex of 

 Pinus Strobus. The aecidium form is Cronartium rubicula. 



(2) Peridetmium Cornui, which occurs in the cortex of Pinus 

 sylvestris, has for its aecidium form Cronartium asclepiadeum on 

 A sclepius Vincetoxicum. 



(3) Peridermium Pini. This is probably the most destructive 

 species, and it is to be regretted that so far the plants have 

 not been determined on which the teleutospores are produced. 

 Until we discover the teleuto form preventive measures must be 

 confined to felling pines that are attacked. 



CHRYSOMYXA 



The genus Chrysomyxa is closely related to the preceding one, 

 in that here also each teleutospore consists of a row of cells, the 

 terminal one of which produces a multicellular promycelium 

 with four sterigmata and sporidia. The sporophore consists of 

 a dense orange yellow cushion-like body of varying shape. The 

 urcdo and aecidium layers are similar to those of the genus 

 Coleosporium. 



CHRYSOMYXA ABIETIS, 1 THE SPRUCE-LEAF-RUST 

 This is a disease of the spruce which is met with through- 

 out the whole of Germany, with the exception of the higher 

 Alpine regions. It occurs on old as well as on young spruces, 



1 Reess, Bot. Zeit., 1865, Nos. 51 and 52, and Willkomm, Die mtkros- 

 kopischen Feinde des Walde.s, 1868, pp. 134 166. 



