ILLUSTRATIONS OF PHYTOPHTHORA INFESTANS. 419 



The spherical resting zoospore remained unaltered, to all 

 appearance, from 4.56 till 6 o'clock, but soon after that was 

 seen to be putting forth a protuberance {t) (6.14 p.m.), which 

 soon elongated into a hypha {v) (6.34) as long as the diameter 

 of the zoospore. At 7.10 this germinal hypha was twice the 

 diameter of the zoospore in length, and a large vacuole had 

 formed in the rapidly emptying zoospore (iv). This vacuole 

 occupied nearly the whole of the cavity at 7.50 — in other 

 words, the protoplasm had nearly all passed into the develop- 

 ing germinal hypha [x). A tiny protuberance on the hypha 

 also indicated an incipient branch, which, however, did not 

 attain any considerable length, and soon became emptied. At 

 11.20 p.m. the state of affairs was as shown in the drawing (z). 

 The whole of the protoplasm was in the apical one fourth or 

 one fifth of the germinal tube, the rest being empty like the 

 zoospore, and having three very thin septa across at pretty 

 equal distances. Whether these septa are really cellulose walls 

 it was impossible to determine. Next morning there was no 

 appreciable change, and the protoplasm seemed to be dying 

 towards evening. 



The other four of the five conidia sown did not develope 

 zoospores ; two of them germinated directly in the manner 

 shown in fig. 7. The development of the zoospores is de- 

 layed or even arrested by direct daylight, even if not very 

 strong, and it is not improbable that in the present case the 

 formation of the zoospores was arrested in the other conidia by 

 the repeated and continued exposure of the preparation during 

 the observations. 



Fig. 5. — In this drawing two zoospores are represented germi- 

 nating on the epidermis of a potato leaf, and one has become 

 rounded off, but has not yet put out a germinal tube. The 

 preparation was obtained by painting the lower surface of a 

 fresh leaf with a camel-hair pencil dipped in rainwater and 

 then passed over freshly developed conidia at the margins of 

 disease-spots on other leaves. At the end of twenty hours the 

 leaf was examined, and numerous zoospores were found on the 

 epidermis, many of which had put forth germinal tubes which 



