340 DISEASES OF FIELD & GARDEN CROPS. [CH. 



is it always wise to say too positively that doubtful 

 characteristics are certainly present ; it is safer under 

 critical circumstances to say the characters appear to be 

 present or non-present. 



The cilia or vibrating hairs of the zoospores of the 

 potato fungus are so excessively attenuated that, when the 

 highest magnifying powers are used, and with the cilia close 

 to the object-glass, it commonly happens that both hairs 

 cannot be seen at the same time : an alteration of the focus, 

 small beyond description, is necessary to see first one, then 

 the other. When a zoospore becomes quiescent and ger- 

 minates, the cilia vanish. They either dissolve or break 

 up into the finest dust dust so small that no figures can 

 express the minuteness of the particles. Now it is well 

 known that all parts of the potato fungus are so potent 

 with life that every visible atom will grow and reproduce 

 the fungus. It is quite possible, then, that, just as every 

 atom of a mycelial thread of this fungus will continue its 

 growth to the perfect form, so every atom of a broken up 

 flagellum perfectly invisible to the eyes even when the 

 highest powers of the microscope are used may be 

 capable of carrying the poison and at length reproducing 

 the perfect form of the fungus in the potato plant. 



We think it would be well if all agriculturists would 

 set apart a small portion of each farm or garden for ex- 

 perimental purposes, each farmer taking a personal, 

 practical, and scientific interest in his own special crops. 



Seeds of all sorts should be selected from the healthiest 

 parents. Indiscriminate seed planting should never be 

 practised. By constantly selecting seed from plants free 

 from disease, hereditary disease might at length exhaust 

 itself and be extinguished. We think it impossible to 

 over-estimate the importance of the fact of the hereditary 

 nature of disease in plants and animals. Mr. Charles 

 Darwin, writing in his Animals and Plants under Do- 

 mestication, vol. ii. p. 7, says : " Unfortunately it matters 



