CONTENTS. Xlll 



Observations of HALES on the blight in hops, &c 84 



Fire-blasts in hops .. ... ... ... ... ... 85 



HALES recognized the influence of evaporation on the life of 



plants ... ... ... ... ... ... ... 86 



The origin of the potato disease is probably similar to 



that of the blight in hops ... ... ... ... 87 



The disease long known ... ... ... ... ... ib. 



It is due, not to a degeneration of the plant, but to a com- 

 bination of external circumstances ... ... ... 88 



It is connected with the weather, and particularly with the 



temperature and hygrometric state of the atmosphere ... 89 

 The life of plants is dependent chiefly on four external 



causes ... ... ... ... ... ... ... 90 



Only one of which, namely, the quality of the soil, is in 



the power of the agriculturist ... ... ... ... 91 



Effects of suppressed evaporation ... ... ... ... ib. 



The fungi and putrefaction follow the death of the plant 92 

 Observations of HALES on the rise of the spring sap in 



perennial plants ... ... ... ... ... ... ib. 



Views of DUTROCHET ... ... ... ... ... ib. 



Objections to these views ... ... ... ... ... 93 



The cause of the rise of the sap is transient, and depends 



on external influences ... ... ... ... ... 94 



It exists, not merely in the spongioles, but in all parts of 



the plant ... ... ... ... ... ... ... ib. 



Experiments of HALES ... ... ... ... ... 95 



His conclusions ... ... ... ... ... ... 97 



Gas is given off by the sap 98 



The rise may therefore be due to disengagement of gas ... 99 



The gas is probably carbonic acid... 100 



[APPENDIX 



