12 DISEASE IN PLANTS. 



extensions of our knowledge, did their work 

 forthwith in disabusing men's minds of old and 

 erroneous notions. To say nothing of numerous 

 smaller misconceptions which still held their 

 ground owing to the stupendous ignorance of 

 plant-physiology which prevailed, we find incom- 

 petent teachers and text-books were still pro- 

 pagating ideas worthy of ancient times. The 

 confusion between oxygen-respiration and the gas 

 interchanges in carbon-assimilation was by no 

 means eliminated even recently, though it can no 

 longer withstand the deliberate onslaughts now 

 made on it. That the roots take up food as such 

 from the soil, and that that food is directly em- 

 ployed by the plant for its nutrition is even yet 

 implied in daily conversation around us ; and 

 although matters have advanced so far that every- 

 one now knows that the substances at the roots 

 must be in solution, ere they can be received 

 into the plant, it sometimes leads to astonishing 

 replies, if we press the question very far as to 

 how the absorption takes place, in an elementary 

 examination of agricultural students. That man- 

 ures are foods to the plant, that sap circulates, 

 that transpiration is of use to keep the plant 

 cool, and wood is a " porous body," etc., are 

 only a few of the misconceptions still current, 

 in a decade that has found publishers for 

 a work advocating that roots are congealed 

 sap, and that the leaves of plants absorb the 

 moisture and dust of the air, and so provide 

 the plant with food, and for a paper explaining 



