the Summer; Rue, Thyme, Pot-Marjoram, and Stone-crop, are often of this Sort. This Diftemper is fomewhat like the Scurvy, Itch, and fuch-like Cutaneous Diftempers, which generally appear about the fame Seasons.

Secondly, We have Plants that are continually blotch'd with Yellow in the Spongy Part of their Leaves, whilst the Sap Veifels are of a pleasant healthful Green; of fuch Sort is the Blotch'd Alaternus, the Orange-Mint, and fome others. To give these Strength, by means of rich Manure, or inarch them into healthful Plants, the Diftemper will be overcome, and the Yellow Colour be chang'd into a lively Green This is fomewhat like the Jaundice in Animals.

Thirdly, We have Plants whofe Juices are fo inveterately poifon'd, that their Distemper is continu'd from Generation to Generation; the Leaves of fome are maculated or spotted, others edged, others blotched, and others ftriped, fuch as the Sycamore, Bank-Crefs, SelfHeal, Borage, Archangel, Water-Betony, and Striped-Sallary; all which bring ftriped Plants from Seed, I think their Cafe is not much unlike what we obferve in fuch Animal Bodies as are afflicted with fuch Hereditary Diftempers as the Evil, the Leprofy, or the Pox fometimes happens to prove. We must obferve however, that all the Seedling Plants I speak of are not affected alike; fome are more ftriped, fome lefs, and now and then some few will come healthful, and be entirely Green in their Leaves. Surely fuch Plants, whofe very Seeds do not escape being infected, could never be, if there was not as due a Circulation

and

and Secretion of Juices in them, as there is in Animal Bodies. I fuppofe 'tis hardly poffible to eradicate fuch Diftempers in Plants, without a confiderable Length of Time, and a vaft deal of fresh Nourishment thrown into them.

This Knowledge leads us partly to the Cure of Distempers in Plants, and alfo will inftruct us a great deal in the Pruning them, and the Seafons for it; nor does it inform us lefs of the Cautions to be taken in the Removal of Plants, or of ftrengthening our Flower-Roots for future Blowing; for it has been experienc'd, that in Plants of the lower Race, when they are cut down near the Root, at a Time when the Sap is in its highest Vigour, fuch Plants have always been weak the following Year and have fometimes perifh'd. The curious Mr. Fairchild obferv'd, that one Summer he had a Bed of Striped Lillies which were rifing to Flower, were in the Height of their Sap cut off by Lightning, and the next Year fcarce one in an hundred was ftrong enough to bloffom; and the fecond Year not above four in the whole Bed were ftrong enough to bloffom: So if we make any great Amputation upon any Tree of our own Growth, when the Sap is in its full Vigour, it will weaken and endanger the Tree.

As an Illuftration of what has been here related concerning the Circulation of Sap, I fhall add a Letter which fome Time fince I fent to Dr. Douglass.

To

To Dr. Douglafs, F. R. S. in Bow-Lane, London.

SIR,

“TH

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66 HE Turkish Method, which has been lately brought into England, of inoculating the Small-pox, has furnish'd me with many Hints which tend to the further "Discovery of the Circulation of Sap in

"Plants.

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"I have in many of my Writings given In"ftances of the Analogy between Animals "and Vegetables, and have as often brought Experiments to confirm the Sap's Circulation, and the Generation of Plants; both "which Difcoveries, the more we know of "them, the more it is in our Power to im66 prove our Fields and Gardens.

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Mr. Fairchild of Hoxton, who has been very diligent and curious in these Enquiries, gave me lately two or three excellent Ob"fervations of his own, concerning the Sap "of Plants: He tells me, that having graf

fed the ever-green Oak, or Ilex of Virginia "upon the common Oak, the Leaves of the "common Oak, which was the Stock, de

cay'd and fell off at the ufual Seafon of the "Year; but the ever-green Oak, which was

"the

"the Cion graffed upon it, preferv'd its Leaves, "and continu'd fhooting in the Winter; fo "that when Trees drop their Leaves, the Sap remains yet in Motion, and is not gone in"to the Root, as fome People think.

"A Cafe of the like Nature I had once "of the Common Laurel, or Lauro-Cerafus, "which I inoculated upon the wild black Cherry; the Leaves of the black Cherry dropt about September, but the Buds of the "Laurel fhot or sprouted fome time after, and "remain'd Green all the Winter.

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"To this we may add what we obferve "of the Mileto or Vifcum, which is not only "an Ever-green, but even grows and ripens "its Fruit a long Time after the Tree it 66 grows upon fheds its Leaves. Mr. Fair"child's Experiment indeed of the Ilex is fuf"ficient to fhew that Sap has a Mode of Cir"culation; and my own Remarks ferve to "confirm it.

"But let us proceed to explain this a little "further, and from hence answer the Obje"Єtion which has been generally made against "the Circulation of Sap, viz. that at the "Fall of the Leaf the Sap always returns to "the Root.

"Whoever knows any thing of the Circu"culation of Blood in Animals, cannot be ig"norant that there are Arteries and Veins "through which it paffes; the first to convey "it from its Fountain, the second to return "it back; and that when this circulative Mo"tion is stopt, Death ensues.

“Every

"Every Plant has Veffels analogous to thefe, which perform the fame Offices: Thofe "Plants which loose their Leaves, and do not grow in the Winter, are like thofe Animals "which fleep in the Winter; but those Plants "which are ever-green and grow in the Win"ter, are like thofe Animals which have a con"tinued Life; and yet both of these have a "Circulation of Juices perform'd thro' Pipes "of the fame Kinds we have mention'd.

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"Among the Animals which fleep in the "Winter-Season, we find that the Urchin or Hedge-hog, the Batt and the reft, are laid "to fleep at the Approach of Cold, which "thickens their Juices; and if we bring these "Creatures, in their fleeping State, into a "warm Room, or near a Fire, they recover "their Motion, and become brifker by de

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grees; but those which have continu'd Mo❝tion, or always an Opportunity of it, are "generally more dull and fleepy in the hotter "Seafons: So that this Difference feems to

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depend upon the Temper of the Juices. And "there are many Experiments which prove "that the Difference of Juices in all Bodies "is caus'd by the different Frame and Tex"ture of thofe Veffels or Strainers they are fil"ter'd through, as I have hinted in another "Part of this Work.

"The ever-green Oak has all the Characte "rifticks belonging to the common Oak, but "the dropping the Leaves; and 'tis only the "different Model of the Veffels in one and "the other that causes the Variety of Ever"green, and the contrary; the Veffels in the "Ever-green difpofe the Juices to act with a

U

"lefs