THE liUSTS OF NOVA SCOTIA. FRASEH. 327 



euheteruredo ; a eu-autoecious, euautouredo; an opsis-heteroeoi- 

 ous, opsislieteruredo, and the other combinations in a similar 

 manner. 



As the tevmiiinliio-v of the spore structures in this paper 

 is that proposed bv Arthur, his definitions of the terms are 

 quoted (Bot. Gax. 39:221. 1905): 



'"'The terms I have to propose apply to the sorus. By sorus 

 is meant the structure Avhich arises from a single fertile hyphal 

 mass or hymenium, either with or without a peridium, now 

 usually called spennagonium, aecidium, uredosorus, teleu- 

 tosorus and kindred names. A simj>le sorus includes the 

 peridium and all true ] araphyses whether peripheral or discal. 



''The new term^ consist of four 'words, with their deriva- 

 tives, one for each of the four stages of nredineal fungi. For 

 the initial stage, usually designated by a cipher and called 

 spermagonium. pycnidium, etc.. I propose pycnium: derivatives 

 pycuial. pycniospores, etc. For the sorus of the first spore- 

 stage usually designated by the Ttoman numeral I, and calle<l 

 aecidium, roestelia, peridermium. etc.. T propose aeciiim : 

 derivatives aecial. aeciospore. etc. For the sorus of the 

 second s])ore-stage, usually designated by the Roman numeral 

 IT, and called uredosorus, etc., I pro]iose nredinium (uredo^ : 

 derivatives uredinal, urediniospores or if preferred uredospore, 

 etc. l"\- rlie sorus of the third spore-stage, usually designated 

 by the IJiiuian uniucral 111. anil called teleutosorus, I ])roposr- 

 tclni))! : il('ri\'nti\'('s telial. tolinsjxirc^. ctp." 



SperiJ I '.ill loll. 



S])ecies have been l)asp(1 largely on uiorphological 

 characters. Tnfectiiu experiments have led to a new conception 

 of species, based ou the ability of the fungi to infect hosts. 

 Thus it has bcMni found that some rusts morphologically alike 

 show diiferences in infecting ])ower. On the other hand it ha^^ 

 I'leeu found that rn<ts which show (lifFerene(s in the choice of 



