316 Transactions. 



Art. XXVI. — Xotes on the Spread of Phytophthora infestans, 

 with Special Reference to Hybernating Mycelium. 



By A. H. Cockayne. 



[Rend before the Wellington Philosophical Society. 4th S< ptenther. l!M»7.] 



The behaviour of a well-known plant-disease under changed 

 environment, or in localities where the disease has not pre- 

 viously existed, is a matter of the most vital importance To 

 the student of plant-pathology. Here in New Zealand we have 

 an exceptionally rich field for the study of the biology of many 

 plant-parasites, for in this country the great majority of our 

 most dangerous plant-diseases are aliens, having been in the first 

 place imported on one or other of their hosts. 



The wide expanse of ocean which separates these islands 

 from other lands forms a barrier which precludes the supposi- 

 tion that they could have been introduced by spores or other 

 reproductive bodies blown hither by the wind. Once intro- 

 duced, the ecological factors for many of these diseases being 

 pre-eminently suitable for their requirements, they have thriven 

 here as well as, if not better than, in their original home. Others 

 which in other countries are justly looked upon as dangerous 

 plant-parasites have, on acclimatisation here, been quite unable 

 to cause sufficient damage to rank them as markedly injurious. 

 Others, again, which in their native country appear to live more 

 or less in equilibrium with their hosts, have, since their intro- 

 duction here, become virulently epidemic, and are the cause of 

 much annual loss both to the farmer and fruit-grower. 



In these notes I shall confine myself to some observations 

 on the ecology of the Irish potato-disease (Phytophthora in- 

 festans). 



Introduction into New Zealand. 



There are no definite records of when and how Phytophthora 

 infestans was first introduced into this country. On the epi- 

 demic outbreak of this disease in November. 1904, Professor 

 Thomas made the following statement : " The same disease 

 ( /'/u/iophthora infestans) appealed some twelve years ago, but it 

 was not so prevalent as on the present occasion." Further, he 

 says, "Moreover, it is no new thing here, having been in the 

 country, to my certain knowledge, lor the past twelve years." 

 Mr. T. W. Kirk, in the report of the Department of Agriculture 

 for 1905, writes, "Twelve years ago there was a mild outbreak 



