stages of" decomposition results are produced eminently 

 calculated to favour the growth and development of fungi. 

 The constitution of a plant suffering from a want of special 

 element must be more susceptible to the attack of fun- 

 goid or parasitic disease than one in robust condition and 

 surrounded by every element of plant food in a suitable and 

 available form to build up, and maintain, its constitution in 

 vigor. A plant like an animal may go on yielding, but, that 

 does not necessarily mean that its constitution is not becom- 

 ing gradually impaired. A Cow may continue to give milk 

 in certain quantities ; but such may be daily decreasing 

 in nutritive value. A coffee tree may continue to yield crop 

 after crop ; but who can, without a scientific analysis, deter- 

 mine, the relative proportions of Lime. Potash and Soda 

 which are wanting in the composition of the bean in each 

 successive crop ? 



Plants have frequently been experimentally grown and 

 have produced a crop, in a strictly artificially made substi- 

 tute for the soil from which many ascertained food requisites 

 were purposely omitted, but the system of plants under a 

 continuance of such circumstances could not possibly be 

 maintained in vigor. 



Leaf disease appears just after heavy rain, at the ad- 

 vent of fair weather. It only lasts a limited time and entire- 

 ly disappears to return under similar circumstances. Is 

 it unreasonable to conjecture that the period of its appear- 

 ance is contemporaneous with those peculiar or special 

 phases of the decomposition of vegetable matters in the soil, 

 namely either the humin and ulmin, or the acid stages. With 

 the advent of fine weather the soil becomes less cloggy and 

 more capable of allowing the entrance or exit of those gases 

 which either retard, or accelerate, the necessary but myster- 

 ious process. If this conclusion has any truth in it, the 

 remedy for leaf disease is not to be found in any outward 







