The Museum Gazette 



is known as to the possible quiescence of parasitic germs and 

 the conditions under which they assume activity. 1 



The conclusions suggested make it evident that in order to 

 prevent the spreading of the disease attention should be 

 given in two different directions. The utmost care should be 

 taken to avoid planting as sets tubers which may have the 

 fungus in them. When evidences of disease appear in the 

 leaves, measures should be taken, either by the use of spray or 

 removal of the affected haulm, to prevent both spreading in 

 the air and downward growth into the young tubers. 



The facts to which we have adverted as to restricted 

 advance prove that some plants are more susceptible than 

 others. It is very common to see a few spots on the leaves, 

 which remain quite local, just as is the case with the attacks 

 on the corolla. 



Notes on the Potato Disease. 



It is said to have first appeared about 1841, near Boston, U.S., 

 and to have spread over Europe four years later. It is not so virulent 

 now as during the first decade of its invasion. 



The brownish patches on the leaves are the first indications of its 

 presence. Under a pocket lens a number of white threads will 

 be seen on the brown patch, especially towards its edges. Under a 

 microscope these threads will be seen to spring singly, or more 

 usually in clusters, through the stomata of the leaf. They bear 

 globular, colourless spores — the conidia or summer fruit. After a 

 spore is produced at the tip of a thread (co?iidiophore), the latter 

 continues to grow in the same straight line, and ultimately produces 

 a second conidium, and so on. A conidium germinates as soon as 

 mature, and produces zoospores (usually six) as soon as it is moistened. 

 A zoospore has a pair of cilia which enables it freely to move about 

 in the water. Finally it settles down and germinates, producing a 

 slender germ tube, entering a leaf either through a stoma or by 

 boring through its cuticle. 



Rainstorms wash the conidia down upon the tubers, the resulting 

 zoospores enter the latter, ^nd are said to form a latent mycelium in 



1 This winter-latency of material which yet retains its vitality is quaintly 

 referred to by Herbert — 



" It was gone 

 Quite under ground ; as flowers depart 

 To see their mother-root, when they have blown. 



Where they together, 



All the hard weather, 

 Dead to the world, keep house unknown." 



