364 



UREUINEAK. 



direction ; their sori form dark spots which break out from 

 beneath the epidermis. The yeHow uredospores have a coat 

 beset with fine spines, and are given off from sori which may 

 or may not be enclosed in a peridium. The sori of the 

 aecidium-stage have no peridium, and are known under the 

 generic name of Caeoma ; they frequently occur on other hosts 

 than tliose of the teleutospores. Pycnidia are produced in little 

 yellow ]tatches. 



Melampsora tremulae Tul. (Britain). The sori of uredo- 

 spores appear as little yellow protuberances on leaves or young 

 shoots of Populus tremida. The dark-brown patches of teleuto- 

 spores appear later on the under epidermis, and where they 



Fio. 196. — Caeoma 'pinitorquum. Section showing four pycnidia, from one 

 of which (xj>) numerous conidia are being discharged. Caioma-pMches are 

 developing beneath the cortical layer, as yet unbroken. (After R. Hartig.) 



occur in large numbers, an early fall of the leaf may result. 

 The teleutospores hibernate in dead leaves on the ground. In 

 spring the sporidia germinate and infect young shoots of Pinus 

 sylvcstris, producing the disease known as Caeoma jnnitorquMm} 

 This disease attacks pine-seedlings, appearing generally on 

 the needles. It is most frequent in plantations from one to 

 ten years old, rarer in those of ten to thirty years, and not 

 as yet observed in older. Pinus sylvcstris is most commonly 

 attacked, but it has also been observed on Pinus montana in 

 Jiitland. After formation of the Caeoma --psitches, the young 

 thin shoots generally die off, but thicker ones become twisted 

 at the place attacked, whence the name " pine-twister " commonly 

 given to this disease. If the leading shoot be attacked, the 

 seedlings may succumb altogether. The disease develops rapidly, 



' R. Hartig, mchfi'je Krankhcitcn d. Wahlhamne, 1S74. 



