331 



DEWBERRY. 



DEXTRINE. 



332 



The Devonian Formation is represented in Belgium and the 

 Rhenish provinces, in Russia, America, and probably also in Van 

 Diemen's Land. 



With regard to the development of this great system, Mr. Jukes 

 saya " The history of the production of the Devonian Rocks seems 

 to be this : At the close of the Silurian period, or during its later 

 portion, great dislocations and elevations took place, by which the 

 Silurian Rocks, and especially the Lower Silurians of the larger and 

 more northerly portions of the British Islands, became much broken 

 and contorted, and in many places lifted up into dry land. Granite 

 was protruded into them in the south-east of Ireland, and probably 

 also the granites of the north-east of Ireland and of the north of 

 England and south of Scotland, were formed at this time. Great 

 denudations also took place, by which some of the granite of the 

 south-east of Ireland (if not that of the other districts) was brought 

 to the surface. Upon the uneven ground thus formed, as it was slowly 

 depressed again, the Old Red-Sandstone was deposited, consisting 

 largely of the detritus produced by this denudation. 



" But in the south-west of Ireland and England neither disturbance 

 nor denudation took place to anything like the same amount, the 

 locality remaining probably a pretty deep sea, in which fine-grained 

 mechanical and some chemical depositions were formed, partly con- 

 temporaneously with the Old Red-Sandstone proper, and partly 

 subsequent to it. 



" If we are allowed to continue this hypothetical history a little 

 longer, we should say that at the close of the Devonian period a sub- 

 sidence of almost the whole country had occurred, and in the sea 

 thus formed was deposited the Carboniferous Limestone, resting in 

 level sheets on the floor of the Old Red-Sandstone, that had filled up 

 and levelled the hollows and inequalities in the older rocks. When 

 the Carboniferous Limestone had been formed, the Coal-Measures were 

 accumulated on the top of it, setting in first of all as thick sandy 

 deposits, and then as alternations of sandy and shaly beds, with an 

 occasional bed of coal. The depression being suspended, and the sea, 

 having been partially filled by the accumulation of the Carboniferous 

 Limestone, was made still shoaler by the sandstones and shales of the 

 Millstone Grit and Coal-Measures, so that, according to gome, it was 

 entirely filled up to its surface, in order to produce a bed of coal, while 

 every one agrees that it must have nearly been so. 



" Depression then recommenced, allowing the accumulation of 

 several thousand feet of coal-measures, all successively produced in 

 comparatively shoal water." 



(Jukes, Physical Geology.) 



DEWBERRY, a kind of bramble, the Rubu caiitti of botanists. 



[RUBUS.] 



DEWEYLITE, a name for Serpentine. [SERPENTINE.] 



DEXA'MINE, a genus of Amphipodous Crustacea, established by 

 Dr. Leach. The following are its characters : Antenna; 3-jointed, 

 the last segment composed of a number of minute joints; first 

 segment shorter than the second ; upper antennae longest. Eyes 

 oblong, not prominent, inserted behind the superior antenna}. Legs 

 fourteen ; first and second pairs monodactyle, with a small compressed 

 hand ; other pairs furnished with simple claws. Tail, on each side, 

 with three double styles ; above, with one small style on each side. 

 Body, (including the head) 12-jointed. (Leach.) 



V, ipinoia. Body shining, the ninth, tenth, eleventh, and twelfth 

 segments produced into a spine ; front produced and bent downwards 

 between the antennae. The first joint of the upper antenna; beneath, 

 towards their tips, have a little spine-like process. Length three- 

 quarters of an inch. (Leach.) 



Dr. Leach says that it is very common on the southern coasts of 

 England, and is often taken by the shore-net, or beneath stones 

 amongst the rocks at low tide. The legs, he observes, are easily 

 broken, which will account for Montagu's having described and 

 figured it (Cancer (Oammarus) tpinomw) without the monodactyle 

 hands. 



DEXIATU.,32, a family of Dipterous Insects of the section Creo- 

 phila-. This family, established by M. Robineau Desvoidy, is com- 

 posed chiefly of Meigen's genus Dexia. The species may be distin- 

 guished from those of neighbouring groups by the greater length of 

 their legs : the body is generally elongated and cylindrical, but some- 

 times thick, depressed, or rounded. The fore part of the head is, in 

 most of the species, furnished with a ridge situated between the deep 

 grooves in which the antenna; are placed ; the antennas are rather 

 short, and the stylet is generally plumose ; the eyes are separated in 

 both sexes, and the males are usually larger than the females. These 

 flies are of inoffensive habits ; they are usually seen on flowers, the 

 juican of which afford them nourishment. 



The chief characters of the genera contained in the Dexiarire are 

 thrown into a tabular form by M. Macquart, in the following 

 manner: 



Genus 1. Protena, St. Fargeau. 

 Proboscis long. 

 ProboBcia short. 



Body cylindrical. 



First posterior cellule of the wings closed. 



Second and third joints of the antennae of equal length. 

 HAT. HIST. DIV. VOL. II. 



Genus 2. Zeu.ria, Meigen. 

 Third joint of the antennas longer than the second. 



Genus 3. Dinera, Desvoidy. 

 First posterior cellule of the wings open. 

 Antennae not extending to the epistoma. 



Genus 4. Dexia, Meigen. 

 Antennas extending to the epistoma. Legs very long, 



Genus 5. Scotiptcra, Macquart. 

 Body tolerably broad, depressed. 



Fore part of the head arched (colours brilliant). 



Genus 6. Rutila, Desvoidy. 



Fore part of the head flat (colours, black or yellow). 

 Stylet of the antennae naked. 



Genus 7. Gymnostyla, Macquart. 

 Stylet of the antennas covered with fine hairs. 



Genus 8. Omalogaster, Macquart, 



Of the genus Prosena Macquart describes only two species, one of 

 which inhabits Europe, and the other is from Brazil. 

 )f the genus Zeuxia but one species is known. 



The genus Dinera contains five species, one of which inhabits Brazil, 

 and the others are found in various parts of Europe. 



The genus Dexia, contains twelve species, almost all of which are 

 European. 



The genus Scotiptera contains two species ; they are of considerable 

 size, and inhabit Brazil. 



Rutila. The species of this genus appear to be confined to Australia 

 they are generally of large size. 



The genus Gymnostyla contains three species, two of which are from 

 Brazil and the third is from Surinam. 



The last genus, Omalogaster, contains four species, all of which are 

 inhabitants of Europe. 



DEXTRINE is a vegetable substance found in the interior of the 

 cells of plants. It can be artificially procured by treating starch with 

 diastase. Mulder has shown that dextrine may also be obtained from 

 cellulose both by sulphuric acid and by diastase. . The quantity of 

 diastase required is extremely minute ; if too mucfc be iised, or the 

 process continued too long, grape-sugar is produced. It is by these or 

 similar means that nature converts cellulose into dextrine, and dextrine 

 or starch into sugar. As in- malting barley, diastase is naturally pro- 

 duced with the starch, there is no reason why it should not in a 

 similar manner be produced in the growing plant, and thus convert 

 the cellulose into dextrine. [DIASTASE.] 



The sap of nearly all plants contains a certain amount of dex- 

 trine, which, having the same chemical composition (C 12 H 10 ) 

 as gum, and in many other points resembling it, has been in most 

 analyses put down as gum. If one equivalent of water (HO) be taken 

 from one equivalent of cellulose (O,, H 21 21 ), two equivalents either 

 of gum or dextrine [2 (C lt H 10 0,,,)] are formed. Thus a part of the 

 cellular membranes may be converted into dextrine by catalysis with, 

 out destroying the cells, if the vegetable sap, while passing through 

 them, contains only a very minute quantity of diastase, or of a sub- 

 stance resembling it. 



Gum and dextrine have been frequently confounded. The most 

 important difference between them is, that the latter may be changed 

 into grape-sugar by sulphuric acid or diastase, while the former is 

 incapable of undergoing that change. 



Dextrine belongs to that class of matters which are taken into the 

 blood ; all the starch taken as food being converted by the gastric 

 juice into it. The gums are not taken up ; they become mere ex- 

 cretions, and are apparently of little or no importance. 



There seems every reason for believing that dextrine is the source 

 of the cellular matter, for it is a universal constituent of all parts 

 of plants. We are justified in assuming that the sap of plants 

 must contain the elementary matter of cellulose in a state of solution, 

 so as to be able to penetrate through the cell-walls, and to supply new 

 substance to increase the number of cells. No material but dextrine 

 is fitted for this office, though in young plants sugar also contributes 

 to it. By the production, during germination, of dextrine and sugar, 

 we are led to believe that the cellulose of the young plant is really 

 formed from this dextrine and from the sugar in the germinating 

 cotyledons. Whilst many full-grown plants do not contain sugar, all 

 contain dextrine, so that the use of the latter in the formation of cells 

 cannot be doubted. 



Dextrine is not merely a source of cellulose, but likewise of starch, 

 sugar, gum, and perhaps other vegetable substances ; it is almost as 

 valuable to plants as protein is to animals, for it is a constituent from 

 which their organism derives its most important products. The com- 

 position of dextrine being C 1S H ]0 10 , the formation of cellulose is 

 accomplished by every two equivalents of dextrine taking up one 

 eqivaleut of water. Thus 



2 (C M H 10 10 ) + HO=C 2 . H 21 2I =Cellulose. 



Starch and gum contain the same elements in the same proportions 

 as dextrine, and hence for their production require merely a re-arrange- 

 ment of the molecules. For an account of the relation of Dextrine to 

 the other secretions of plants, see the article SECRETIONS, VEGETABLE. 



