8 



SCIENCE OF GARDE2?ING. 



to imbibe as well as to exbale moisture, by plunging the 

 bands in water wben suffering from thirst. 



As all manner of cutaneous, and even internal diseases 

 result from the obstruction of the pores in the animal 

 system, so plants can never be healthy when their pores 

 are in any way prevented from acting regularly. An imdue 

 jjressure of stiff soil about the roots, and a deposit of soot, 

 dirt, and dust on the leaves, are alike injurious. Rains 

 will often remove all the latter impurities from plants that 

 are growing in the open groimd; but a powerful occasional 

 syringing, or washing with a garden-engine, will be exceed- 

 ingly useful in dry, dusty weather ; and for plants in pots, 

 that are kept in the house, the same process, or sponging 

 the leaves carefully, will be highly beneficial at times. 



5. — Scqy and Pulp, 



The liquid matters imbibed by the spongelets and pores 

 of plants, and transmitted through their system, acquire, 

 as soon as appropriated, the name of sap ; and after the 

 two-thirds of the more watery constituents of this have 

 been thrown off by evaporation, the remaining third, which 

 is like the blood of animals, will be consolidated into a 

 thicker consistence, termed pulp. The sap of plants then, 

 is the food w^hich they have taken into their system in 

 its crude state. Being diffused through the stems, and 

 elaborated in the leaves, and the mere water discharged 

 through the pores, it becomes pul}). This last, being the 

 vital part and substance of plants, determines, by its abun- 

 dance or deficiency, their healthiness and strength. If too 

 little solid matter is taken up by the sap, (as will be the 

 case in poor soils,) the plants will be weakly and yellowish; 

 or if the amount of light and air supplied to the plants be 

 insufficient to sepa,rate the wputer}^ from the substantial 

 ])arts of the sap, and to bring it to its proper consistency, 

 tlie shoots will become feeble, drawn, w^antiug in colour, 

 and the leaves pale and tender. 



Palp is chiefiy composed of the carbon or charcoal taken 

 up by the sap, and is itself of a dark blue colour ; but 

 the transparent tissue of the leaf in which it is enclosed 

 being more or less yellow, the combination of the two 



