164 



THE GARDENERS' CHRONICLE. 



[Mar. 16, 



§ 1. The particles of which all matter consists being 

 subject, by the law of attraction, to form solid bodies, are, 

 in the absence of a modifying agent, unfavourable to that 

 condition which admits the action of other-essential agencies 

 in growth. The soils employed for plants in pots being 

 circumscribed, are subject to the force of attraction, by 

 the increased pressure of their parts towards and upon 

 each other. 



§ 2. As the force of attraction in matter, implies a 

 division of its parts to be attracted (or vice versa), it also 

 implies an agent capable of acting singly upon its parts. 



§ 3. The force of attraction, by the pressure or cohesion 

 of matter, being in proportion to the number and closeness 

 of its parts in any given body, it follows that any arrange- 

 ment by which such parts are diminished or increased, 

 must necessarily be a modifying power, or agent, whereby 

 the force of attraction is governed. 



§ 4. The primary agent in Nature, which operates upon 

 the form or arrangement of matter, previous to its decom- 

 position, or affinity, is mechanical force.— (Herschel). 



§ 5. If the attraction or cohesion of matter may be 

 modified (§§ 3 and 4) by mechanical agency, it maybe 

 inferred that such a modifying power or agent is essen- 

 tial to the condition of other agencies acting upon matter. 

 The proportions of soils in pots being subject to attrac- 

 tion by pressure, increase the force of attraction by lessen- 

 ing the distances of the individual parts, and diminish the 

 force of attraction by increasing the distances of such 



parts (§ 3.) 



§ G. As matter, when circumscribed, is subject to an 



undue attraction of its parts (§ 1), and as mechanical 



agency is a modifying cause of attraction (§§3 and 4), it 



may be assumed that a just mechanical arrangement is 



essential in all soils employed in growing plants. 



§ 7. As the force of attraction is in proportion to the 



number of parts in any given body, (§ 3), and is inversely 



as the distances between such parts, it follows that me- 

 chanical agency should be strictly in proportion to the 

 number of such parts. 



§ 8. All elementary substances are capable of entering 

 into combination with each other only in fixed or definite 

 proportions, and not arbitrarily. (Herschel.) 



§ 9. What is this true of combinations may be assumed 

 to be true of mixtures ; and therefore the proportions of soil 

 in which plants are potted should also bear a strict relation 

 to each other. 



§ 10. As the soils in which plants are potted may be 

 acted upon by other agencies, only according to their 

 uniform condition, — 1st, mechanically (§7); and 2d, 

 chemically (§ 8) ; it may be assumed that a law of mutual 

 relation is the only true basis of a perfect arrangement of 

 soils for the growth of plants. 



§11. The fitness of pots for a perfect arrangement of 

 soil, will be in proportion to their uniform admission 

 (externally and internally) of the mechanical, chemical, 

 atmospherical, and solar agencies, essential to the support 



of plants (§9). 



$ 12. As the mechanical and chemical properties of 

 soils are modified by atmospheric and solar action, the 

 latter exerting an opposing tendency upon the former, it 

 may be assumed that the mutual relation or counterbalance 

 of these opposing agencies to the growth of plants con- 

 stitutes the law of equilibrium, by which the vital elements 

 of support to plants are held in solution for such period as 

 their organic structure, or assimilative power demands. 



§ 13. As all plants are sustained by agencies peculiar 

 to their organic structure, and possessing a mutual relation 

 and dependency, it is shown by § 8, that the absence of 

 one agent cannot be supplied by the excess or modification 

 of another. — William Wood, Pine-apple Place. 



( To be continued.) 



PLAN OF A MELON PIT. 



By Mr. R. Glen-denning, Nursery, Turnham-grbbv. 



Mr. Knight has very justly remarked that " there is 

 not any species of fruit at present cultivated in this 

 country which so rarely acquires the greatest degree of 

 perfection which it is capable of acquiring in our climate 

 as the Melon." * 



One of the great evils attending the common mode of 

 producing the Melon in this country is the practice of 

 raising them on dung-beds, where the roots are permitted 

 to descend into the ra nk decomposing material under 



* Knight's Hort. Papers, p. igi. 



them ; the plants, of course, grow very luxuriantly, in 

 consequence of receiving an immense supply of impure 

 and improper food, which is a fact well known by all 

 practical gardeners. In order to obviate this evil, I have 

 been employed by a scientific gentleman in this neigh- 

 bourhood to design a pit for the culture of the Persian 

 varieties of Melons ; his object is to produce them in the 

 highest possible perfection, which I am quite sure cannot 

 be accomplished on a common hot-bed, for Persian Melons 

 are much more difficult to manage than the kinds in 

 general cultivation. 



T^" 



Elevation of the 

 line A A. 



1 



EXPLANATION 

 • A, Burbidge and Healy's Boiler. 



b b, Iron troughs, c c, Pipes. 

 d d, Iron troughs as at b b, in Plan. 

 * e, Pipes as at c c in P Ian. 



/,/, Copper tubes fastened to the troughs to admit 

 steam when required. 



This pit is intended 

 for Melons in summer, 

 and to preserve Pelar- 

 goniums, or other plants 

 in winter. As the ob- 

 ject in constructing it 

 is more for the purpose 

 of experiment than the 

 permanent culture of Me- 

 lons, I have designed it 

 go that Pines may be sub- 

 stituted without any altera- 

 tion whatever ; indeed, any 

 kind of plant, which such a 

 Structure is capable of re- 

 ceiving, and at the same 

 and a warm temperature, 



OF THE PLAN. 

 g, Wire-trellis on which to train the plants. 

 //, h, h, Convenient places for the growth of Seakale, 



Rhubarb, or Asparagus, or keeping tubers of any kind 



during winter. 



LINE 



> ENTOMOLOGY.— No. LVI. 

 The Poplar-gall Aphis (Eriosoma burs aria, Linn.} 

 — Having recently given the histories of the Eltn- 

 tree-gall Aphis and the American Blight, the economy of 

 another species, which is a genuine Eriosoma, may not 

 prove uninteresting, especially as it is the animal which 

 led to the destruction of the Poplars at Evesham. In the 

 early part of August and September, I have frequently 

 observed excrescences upon the midrib and stalks of the 

 Poplar leaves (fig. I), which are invariably at the back- 

 if the seeds of the foot-stalk be twisted in contrary direc- 

 tions, the suture in these galls will readily open, and the 

 contents will be exposed to view. The galls are green 

 with a rosy tint, more or less convex, with an irregular 

 surface, and very thick comparatively; they generally 

 contain a very considerable number of wingless indi- 

 viduals, varying in 6ize ; and I have seldom found more 

 than four or five winged ones in them. The inner surface 

 is covered with liquid globules, powdered over and re- 

 sembling a vast number of eggs of all sizes, which soon 

 dry up and disappear on being exposed to the air and 

 light ; the old exuviae are also scattered about, and amongst 

 them I detected some young Eriosomas with remarkably 

 long tails (fig. 3), which were white, and appeared to be 

 of a cottony substance ; and it seemed as if the skins on 

 moulting had been strung upon this appendage, for I have 

 little doubt that the six minute claws visible at short dis- 

 tances are the skins from the six legs, in which case there 

 is evidence of the specimen represented having moulted 

 at least thrice (fig. 2). These little apterous Eriosomas were 

 very pale-green, with black eyes and short 4-jointed 

 horns. The winged specimens (fig. 5) were also very pale- 

 green, the head and thorax dusky, the eyes black, the 

 horns rather short and 6-jointed, with a seventh joint or 

 minute tubercle at the inside of the apex ; they were 

 powdered over with pearly white, and the apex of the 

 abdomen was woolly and destitute of tubes (fig. 4) ; the 

 wings were colourless, with a large pale fuscous stigmatic 

 spot, a large marginal cell, with three oblique nervures 

 beyond, the first not forked at the apex (*), and the 

 second and third uniting at the base; in the inferior wings 

 the basal nervure forms a trident; the legs are short, 

 especially the anterior, and slender ; the feet are two- 

 jointed, the basal joint minute, the other terminated by 



two claws. 





I 



time requiring " protection 

 may be very advantageously 

 introduced, the hot- water apparatus being so contrived 

 as to command both bottom and surface-heat, either se- 

 parately or conjointly. For the purpose] of supplying 

 soft water for the] plants, I have placed a slate cistern 



at one end of the pit, in 

 order to collect the rain- 

 water from the roof. The 

 soil, if permitted to come in 

 contact with the iron troughs, 

 would, of necessity, become 

 dried, and totally unfit 

 for the roots of any plant. 

 With a view to obviate this, 

 I have placed rough flint, or 

 ■ other stones, over the bot- 

 tom of the bed, and around 

 the troughs, to prevent im- 

 mediate contact, and at the 

 same time, to admit of a more 

 nniform"diffusion of heat over the bottom of the pit, so 

 that the soil which rests upon it may be more regularly 

 heated. The other advantages and conveniences of this 

 pit will be apparent from the above plan and section, with- 

 out further remark. 



The Poplar and Elm-tree galls are formed by a 

 wingless female, which in the spring fixes upon a bud or 

 stalk, and, piercing it, the extravasation of the sap 

 causes the vegetable matter to assume an unnatural 

 and distorted shape, and gradually expanding as the 

 insect buries itself deeper in the tender tissue, lt,8 * f 

 last completely enveloped. There she becomes the 

 parent of a large family, sometimes producing eight 

 daily ; and by giving birth to young Eriosomas instead 

 of laying eggs, the brood increases at a prodigious 

 rate j for they grow rapidly, undergo their moulungs 

 at very short intervals, each one speedily ^ ecoml ^ 

 a mother in its turn ; and at a later period of the 

 year winged females appear : so that before the original 

 founder of the colony dies she is surrounded by a numerous 

 offspring, removed by many generations. Here, as, 

 indeed, everywhere, we see the wisdom of the Creator 

 his works : the duty of the first female being to form a 

 dwelling for her family, she is unprovided with wings— 

 they would be an encumbrance to her, and it is even pro- 

 bable that their development might diminish her fecunmiy, 



but when the family has attained sufficient extent winge 

 females are perfected, which, led by instinct, depart iro» 

 the place of their birth, to disperse their progeny over w 

 face of the earth ; these are always so different in »PP e * 

 ance, and vary so essentially in the anatomical struct" 

 of the thorax, that, knowing them to be of the same 

 species, one would never imagine they were of the same w • 

 In all probability, the expansion o f the ga **™»^ 

 crack, or an entrance may be made by insecu tor 

 birds or ants, wasps and other insects, which, » ttrac , ot 

 by or feeding upon Aphides, may gain access to the ini 

 through the natural suture, and thus the ringed spec 

 mens are enabled to escape from their prison and « * 

 their way to other and distant districts to deposi t e« j 

 which will again provide for a succession ot W1D & 





which will again proviuc «« * D "^° ^hese helpl«» 

 and viviparous females the ensuing spring. Inese uc g cial 

 animals seem to require the protection of an ar 

 covering to guard them from the extremes of > ieat kept 

 cold, and unless the inner surface of the g»» J" tbat 

 moist, in the manner already alluded to, it is probable 





