mVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 



995 



Alternation of Generations in Gymnosporangium.* — Oersted lias 

 already sliowu that the sporidia of Podisoma sahince, parasitic on 

 Juniperus sabina, sown on Pijrus communis, give rise to Boestelia can- 

 cellata ; those from Podisoma jimiiyerinum, parasitic on Juniperus com- 

 munis, to Boestelia cornuta when sown on Sorbus aucuparia ; and those 

 of Podisoma clavariceforme, parasitic on J. communis, to Boestelia 

 lacerata when sown on Crakegus oxyacantha, and to B. penicillata on 

 Pyrus Malus (this last is, however, believed by the present writer to 

 be an error). 



A long scries of experiments, conducted by Dr. E. Rathay, have 

 led him to the conclusion that: — 1. The Podisoma sabincB on Juniperus 

 sabina, and the Boestelia cancellata on Pyrus communis, belong to the 

 same species. 2. Tlie Boestelia cornuta on Sorbus aucuparia belongs 

 to the Podisoma juniperinum on JunijJerus communis ; and that, contrary 

 to expectation, to the same teleuto-form belong also the Boestelia 

 penicillata on Pyrus 3Ialus and Sorbus Aria, and the Boestelia on 

 Cydonia vulgaris. 3. The Podisoma clavariceforme on Juniperus com- 

 munis, the Boestelia lacerata on Cratcegus oxyacantha and monogyna, 

 and a distinct Boestelia found by the writer on Pyrus communis, and 

 another on Sorbus torminalis, all belong to the same species. 4. No 

 result followed from sowing the sporidia of Podisoma sabince on 

 Mespilus germanica, Cratcegus oxyacantha, G. monogyna, Pyrus Malus, 

 Sorbus Aria, or S. torminalis ; or those of P. juniperinum on Mespilus 

 germanica, Cratcegus oxyacantha, C. monogyna, Sorbus domestiea, or 

 S. torminalis ; or those of P. clavariceforme on Mespilus germanica, 

 Pyrus Malus, Sorbus domestiea, or S. Aria. 



In order to simplify the nomenclature, Oersted united these series 

 of teleuto-forms and fecidio-forms into the genus Gymnosporangium ; 

 and to the three species occurring in Denmark he gave the names 

 G. fuscum, conicum, and clavariceforme, corresponding to the teleuto- 

 forms Podisoma sabince, juniperinum, and clavariceforme. 



E. Eathay states that the teleutospores of P. clavariceforme are 

 mature earlier than those of P. sabince and juniperinum ; and that the 

 same is the case with regard to tlie maturity of the sperraogonia and 

 ajcidia of tlio corresponding aicidio-forms. He gives the following 

 table of all the species on which both forms of the three species have 

 at present been found to be parasitic : — 



Hosts of Teleuto-form. Hosts op .^cidio-form. 



GijTnnosporanguiin fuscitm I Juniperus sahini L. 



DC, Oerst. | 



Gymnosporangium conicum Juniperus communis L. 



DC, Oerst. 



Gymnos^pornntiium cinvn- 

 riivfurmc DC, Oerst. 



Jnniprrnx communis L 



Pyrw? communis L. 



Sorbus aucuparia L. 

 Aronia rotuwlifolia Pcr.s. 

 Pyrus Malus Tj. 

 Sorbus Aria Crtz. 

 Cydonia vulgaris Pcr.s. 



Cratwgus oxyacantha L. 

 Crata:g>is mono<jyiM Jac4]. 

 Pyrus communis L. 

 Sorbus tonninalis Crtz. 



* *Oestcrr. Dot. Zeitr^clir..' xxx. (1880) pp. 211-4. 



