No. XV.B.] APPENDIX. 247 



Potatoes which ripen eai-ly run their course before the insect appears 

 in gi-eat profusion, and consequently escape : hence all early sets are best 

 adapted for planting, and early planting, to enable them to escape the 

 malady. Ajs the period at which potatoes ripen is well known to agricul- 

 turists, I need not call further attention to this subject. 



The unequal capacity of different varieties to resist its deleterious 

 agency I find to depend upon the extent which each deviates from its 

 normal type ; and the more highly cultivated the plant is, the more prone 

 is it to disease. This is not only true of the potato, but is also true of all 

 other plants attacked by the vastator. 



I beg to call attention to the following extracts from my work upon 

 this subject : — 



" Every particular kind of potato, however, is not equally prone to 

 disease, or rather, I may say, to carry its individuality or peculiarity into 

 its diseased condition. The supposed original Chelsea potato seems to 

 resist the action of this malady nobly, the disease only attacking it from 

 leaf to leaf, and not affecting so materially the underground stems. I 

 have carefully examined this specimen, in order to observe how it would 

 be attacked, and I found that the large leaves were all destroyed, and that 

 the disease progressed from the large leaves to those somewhat smaller, 

 and so crept on till it progressed to the top. In consequence of this mode 

 of attack, the main shoot and all the lateral shoots were green, healthy, 

 and vigorous, and the plant appeared to a casual observer to be quite 

 healthy; and the latge leaves, or those out of sight, being alone 

 destroyed up to October the 16th, the plant was still growing vigorously. 

 At the Horticultural Society's Gardens, on my first visit, Tlhde's wild 

 potatoes showed the disease only on the leaflet, and on a subsequent occa- 

 sion there was also one other leaf curled. In both cases I removed the 

 diseased leaf, and found that they were inhabited by a parasite, which I 

 shall hereafter describe. No two kinds of potatoes show the effects of the 

 disease equally; and it is generally supposed that that potato which 

 ripens in the early period of the year, manifests the malady less than 

 those which ripen later, so that the early shows are tolerable free from it. 

 On examining a field in which many varieties are cultivated, every sort 

 will be found to exhibit the malady in its own way : some varieties will be 

 moi-e diseased than others, and some will die down earlier than others. 

 Some potatoes require more leaf than others, and I have no doubt that 

 those which require an extensive crop of leaves are more prone to the 

 disease than others. At the Horticultural Society's potato-ground, many 

 kinds were found to have the tubers quite healthy, while others were much 

 diseased. The white-eyed I'ed was of the former class ; the mouse of the 

 latter. I dare say that it will be found that the more nearly the tuber 

 i-everts back to Gerard's old type, the more capable it will be of resisting 

 the disease. The white-eyed red was in some respects similar to the old 

 species in the Chelsea garden. I applied at the Horticultural Society's 

 Gardens for a return of the relative number of good potatoes to bad ones 

 in each sort cultivated by them, but was unable to obtain it, as a similar 

 return was ordered to be printed in their own Transactions." 



When I made the application for this return, I thought it a strange 

 coincidence that two individuals should at the same moment have desired 

 the same return, especially as the Society might have rendered the return 



