168 NOTES AND MEMORANDA. 



Wlieu a crop of lettuces is suddenly invaded by Peronospora, wBere 

 must the cause of it be sought ? The cause ought to be attributed to 

 the surrounding weeds, to the groundsel, artichokes, &c., already 

 having the parasite. Sometimes, however, none of these plants are 

 found in the neighbourhood : the spots are then produced by the 

 germination of dormant spores or oospores, the second manner of 

 reproduction of the parasite— oospores which germinate after a long 

 time of repose, and may be preserved in the soil or on its surface, 

 only requiring a little damp and heat in order to germinate. 



These oospores are developed in the tissue occupied by the filaments 

 of the mycelium, and dried up under its action. They are frequent 

 upon groundsel, but very rarely appear on the lettuce, although their 

 existence there is most probable. 



If a transversal section is made of the leaf attacked, we see the 

 mycelium creeping between the cells, and putting forth elongated 

 ovoid suckers : when the exhausted tissue dies the mycelium dis- 

 appears, and is itself the cause of its death. It is this change which 

 is met with during the summer. 



If the plant is more completely invaded, the conidiophorous fila- 

 ments are more rare on the surface of the leaf, which is paler, and the 

 leaf dies entirely without drying up ; it grows soft, and turns brownish. 

 This modification is generally produced outside the external leaves ; 

 and it is this which is found during the winter. 



M. Max Cornu considered it possible to find in the cultivation of 

 the plants and in the history of the parasite a means of guarding 

 against its attacks ; and presented to the Academy later some general 

 considerations on the subject.* 



Disease of the Coffee-tree originating from Anguillulce. — A disease 

 has made its appearance in Brazil which rapidly kills the coffee- 

 tree, an apparently healthy tree dying within a week from its leaves 

 withering and falling off."! 



On examining the roots of the trees they are found to be com- 

 pletely covered with swellings the size of hempseed, the root present- 

 ing the general appearance of a vine attacked by the Phylloxera. 

 These swellings contain cysts with hyaline walls, which in their 

 development destroy the fibro-vascular structures. Within the cysts 

 are a number of ovules in all stages of development ; those in an 

 advanced stage are somewhat reniform, with a hyaline enveloping 

 membrane, and within them is found coiled up a small Anguillula, 

 about • 25 mm. long, and without any trace of sexual organs. Each 

 cyst contains from forty to fifty ovules, or about 30,000,000 Anguilluloe 

 per tree. 



The animalcules, which are not reviviscent, when developed 

 escape out of the cyst, leaving the cavity open, and the roots soon rot 

 and are invaded by cryj)togams.} 



* 'Comptes Eenchis,' vol. Ixxxvii. (1878). 



t M. C. Jobert, in 'Comptes Rendus,' vol. Ixxxvii. (1878) p. 941. 



X See also a paper by the Rev. R. Abbay, on " Hcmilcia vastatrix, the eo-called 

 Coftee-leaf Disease of Ceylon," in 'Jour. Linn. Soc' (Bot.), vol. xvii. (1878) 

 p. 173. 



