Plant Sanitation. 



328 



[April, 1910 f 



over, would only be warranted if he had 

 grown the fungus in pure cultures, and 

 there seen one form develop from 

 another. As far as can be determined 

 from his publications, he has not done 

 so. 



It is true that Carruthers records a 

 series of infection experiments, where 

 in many cases he produced the disease 

 in stems as well as in pods by inocul- 

 ating them with one of the three kinds 

 of reproductive organs, But since these 

 inoculations were not made with pure 

 cull 11 res, and since the experiments were 

 conducted on estates on which the 

 disease was prevalent, while no control 

 plants were kept (trees treated in ex- 

 actly the same way as the inoculated 

 ones, except that no fungus was intro- 

 duced), these results are not so convinc- 

 ing as to remove the doubt which yet 

 remains on many questions. We may 

 consider some of these questionable 

 points. It is possible that Carruthers 

 introduced into the wounds other coni- 

 dia besides those he meant to use, as he 

 himself refers to the difficulty of grow- 

 ing the fungus in pure cultures on 

 account of bacteria and fungi. 



Of the Nectria peritheeia he says :— 

 " They are to be found only on dead 

 wood or dead patches of dying branches 

 and stems." 



Moreover, Peteh says: " The Nectria 

 on the stem agrees with Nectria stria- 

 tospora, Zimm. It is perhaps the com- 

 monest Ceylon Nectria, and has been 

 found on tea killed by Massatia theicola, 

 tea with branch canker, felled Albizzia, 

 etc" 



Both these statements make it very 

 likely that this Nectria was not a para- 

 site, but a saprophyte. 



Whereas Carruthers believed the form 

 found by him to be Nectria ditissima, 

 Tub, according to Petch the peritheeia 

 on the bark bear a close resemblance to 

 Nectria striatospora, Zimm.; numerous 

 examples, collected by Thwaites in the 

 Herbarium, have been named by Berke- 

 ley either N. cinnabarina or N, san- 

 guinea. 



The two forms observed by Howard 

 were named by Massce Nectria theo- 

 bromm and Calonectria flavida. The des- 

 cription of Neetria theobromw has just 

 been published. Howard could infect 

 trees by introducing ascospores of both 

 forms into wounds. In the earlier stages 

 of the disease he observed white pustules 

 in the cracks of the diseased bark, con- 

 sisting of conidiophores bearing Uni- 

 cellular conidia and Fusariumlike, multi- 

 cellular conidia. Although he thought 

 it highly probable that both conidial 



forms and the ascus form belonged 

 together, he regarded it as uncertain, 

 until he should have proved it by fur- 

 ther investigations which were in pro- 

 gress when his article was published. 

 Apparently he has not completed his 

 research as Stockdale observed recently 

 that an exact knowledge of the life- 

 history of N. theobroma? and Cat. 

 flavida was not yet complete and in- 

 vestigations would be continued, 



The Nectria noted by Hart on canker 

 spots of cacao trees appeared also to be 

 Nectria Theobromce. Von Faber also 

 found a Nectria on bark from canker 

 trees in the Cameroons. To judge from 

 his figures and description, this form is 

 different from N. Theobroma?, and 

 certainly distinct from the one observed 

 as a saprophyte in Surinam. F. Faber 

 had no opportunity of making infection 

 experiments and could only study fixed 

 material, so that he could not cultivate 

 the fungus. Therefore, it is a mere sup- 

 position, that this Nectria is parasitic 

 on cacao. 



From the foregoing it is evident that, 

 although several forms of Nectria have 

 been considered to be the higher fructi- 

 fication of the canker fungus, none has 

 been definitely proved to be so by experi- 

 ments to which no objection can be 

 taken. 



We must put another important ques- 

 tion which has not yet been solved : 

 What is the cause of the pod-disease ? 



With conidia, ascospores or pieces of 

 cankered bark, Carruthers could pro- 

 duce the disease in pods. It also spread 

 to the pod from a diseased spot in the 

 bark, and reverted from a pod to the 

 stem. By placing pieces of diseased 

 pods in the bark, canker could be pro- 

 duced in it. 



Now in his two first reports Carru- 

 thers discusses his observations on dis- 

 eased pods. The mycelium he found 

 in them was different from that in the 

 stem ; in cultures made of them a Pero- 

 nospora developed (in a later report 

 he calls it Phytophtora), which also 

 was observed on pods in the field. He 

 therefore made this fungus responsible 

 for the disease. In his third report, 

 however, he came to quite a different 

 conclusion. On further examination he 

 had found the small canker conidia 

 between the large masses of Peronospora- 

 (Phytophtora-) Sporangia ; the first were 

 sometimes found alone but yet nearly 

 always speedily associated with Peronos- 

 pora ; hence he supposed that Peronos- 

 pora lived as a saprophyte on the tissues 

 killed by the canker. 



