673 



SPIMGRADA. 



SPIRAL STRUCTURES. 



It is found on the borders of Lake Laach, near Andernach on the 

 Rhine. Its analysis by Klaproth gives 



Silica 43-0 



Alumina 295 



Soda 19-0 



Lime 1'S 



Peroxide of Iron 1 - 



Sulphuric Acid 2'0 



Water . . 2'5 



98-5 



SPINIQRADA. [ECHINODERMATA.] 

 SPINIPORA. [MlLLEPOBID^.] 



SPIRAEA, a genus of Plants belonging to the natural order Rosacece, 

 tribe Spiracere. The name occurs in ancient authors, and is supposed 

 to be derived from <rimpa, a cord, in allusion to the fitness of the 

 plants for twisting into garlands. The genus is diffused through the 

 temperate parts of the northern hemisphere, and is characterised by 

 having a 5-cleft permanent calyx ; stamens 10 to 50, inserted ill a torus 

 with the 5 petals, which are inserted into the calyx ; carpels sessile, 

 solitary or several, rarely connected into a capsule; seeds 2-15, pendu- 

 lous, very rarely ascending. _ The species, upwards of 50 in number, 

 form -mall unarmed shrubs or perennial herbs ; leaves usually simple, 

 sometimes pinnately cut ; flowers white or reddish. They are found 

 in Europe, North America, Siberia, China, and the Altai and Himalayan 

 Mountains. 



8. Utmaria, 55eadow-Sweet, is found in our meadows ; and S. fili- 

 pendula on our downs, &c. Pigs are said to be fond of the tubers 

 of the roots. Several of the species are astringent, and might be 

 used in tanning. S. trifoliata is sometimes called Ipecacuanha de 

 Virginia, being employed as an emetic. 



SPIRAL STRUCTURES. In the development of the tissues of 

 plants and animals two tendencies are observed ; the one simply that 

 of extension in a vertical direction, the other is that of curvation, 

 mostly resulting in the production of a spire. The tendency to develop 

 parts in a spiral direction, though much more prominent in the vege- 

 table than in the animal kingdom, is by no means confined to it. In 

 the ninth volume of the ' Anuales des Sciences Naturelles,' Maudl has 

 shown that all the tegumentary appendages of animals, ns the scales, 

 feathers, hair, etc., have a spiral arrangement, and that many of the 

 internal organs are subject to the same law. The tendency to develop 

 structures in a spiral form appears to be dependent on some of the 

 higher laws regulating organic life ; and in this view the subject has 

 been investigated by recent botanists. Giithe,' the German poet, in 

 his ' Essay on the Spiral Tendency of Vegetation,' published in 1831, 

 gives the following view. He supposes that there is a dependence of 

 those properties which plants possess of resisting external agents, and 

 of enduring for a length of time, upon those parts that are developed 

 vertically, while the nutritive and reproductive functions are connected 

 with spirally-developed structures. In support of this generalisation 

 he adduces a number of facts. If a branch of an ash-tree is injured, 

 so that the lower parts become over-nourished, it possesses a tendency 

 to become spiral. When the leaves of the Italian poplar are injured 

 by insects, the petioles become twisted. Spiral vessels exist in greatest 

 numbers in the growing parts of plants, as the alburnum. They also 

 exist in greater numbers in the higher plants, the lowest possessing 

 none. A spiral arrangement of parts is also much less observable in 

 the lower than in the higher groups of plants. The organs of nutrition 

 and reproduction, the leaves and parts of the flower, have normally a 

 spiral arrangement. Von Martins, Mohl, and others, have also written 

 on the general theory of spiral structure. 



Cellular tissue was at one time supposed to consist of plain simple 

 cells, but the researches of later botanists have proved that the cells 

 of this tissue are often furnished with fibres, which are twistod in a 

 spiral manner. This spiral fibrous tissue is abundant in the roots of 

 orchidaceous plants, in the seed-coats of many plants, and in the 

 linings of the valves of almost all anthers. Spiral fibres, independent 

 of any cells, and apparently surrounded by vegetable mucus, have 

 been found in the testa of the seeds of Collomia linearis. lu the seed- 

 coats of the seeds of species of Blepharit and Acanthodium spiral fibres 

 inclosed in membranous tubes are found in very great abundance. 

 The organs called elaters, which are contained with the sporules in the 

 conceptacles of Jungermannia, consist of spiral fibres surrounded by 

 a tube. In the reproductive cells of both animals and plants a spiral 

 arrangement of the protoplasm is often observed, and as a rule the 

 spermatozoa and spermatozoids of plants and animals arc developed in 

 this form. 



In the vascular tissue of plants is found a tissue, which on account 

 of its spiral structure has been called Spiral Vessels. These vessels 

 appear to be little more than fibrous cellular tissue elongated, the 

 parietos of the cell forming an elongated tube, which is tapering at 

 each extremity, and contains within it one, two, three, or more spiral 

 fibres. This tissue is exceedingly abundant in exogenous and endo- 

 genous plants, but is not found in the lower families of Oryptogamia. 

 It exists however in Ferns, Lycopodiacecp, and quietacece. It is only 

 sparingly found in Conifera. These spiral fibres "possess the power 

 of moving when touched. 



The spiral tendency is developed in the structure of the stem and 

 leaves of plants. The part of the latter which exhibits this structure 



is the petiole, and in this organ all forms of the spire may be seen, 

 from a single twist to the complicated spires observed in the organs 

 called cirrhi. In most plants these cirrhi assist them in climbing, 

 their structure adapting them to this purpose. The spires of the 

 cirrhi twist in some from right to left, in others from left to right ; 

 and in the cirrhi of the genera Passiflora and Bryonia the direction 

 changes several times in the course of the spire from right to left and 

 from left to right. 



In the structure of many of the Confervas a spiral arrangement of 

 the tissues is observed, especially of those which approach the animal 

 kingdom in their movements, as the Oscillatorite. The sete which 

 support the conceptacle of Jungermannia, and which contain the 

 spiral elaters before mentioned, possess in many instances a spiral 

 structure. This is also occasionally developed in the same organ in 

 mosses, a remarkable instance of which occurs in Funaria hygrometrica. 

 In this moss the sette are quite straight when young, but assume the 

 spiral structure as they increase in age. In this setae the spire turns 

 in two directions : from the base about two-thirds up the stem it goes 

 from right to left; it then becomes quite straight, and turns in the 

 opposite direction from left to right. A curious property is possessed 

 by these seta; when the capsules are ripe. If the upper part of the 

 spire is moistened, the capsule commences turning from right to left ; 

 but if the lower part only is moistened, it turns from left to right. 



The entire stems of plants are frequently spiral, as is seen in the 

 plants which are called Climbers. These plants, by reason of the 

 spiral arrangement of their tissues, twine around the nearest objects, 

 whether organic or inorganic. In most of them the winding of the 

 spire is to the left side, but in a few the turning is to the right. 

 Amongst the former are the genera Cuscuta, Phaseolus, Dolichos, 

 PassiJtora,Sanisteria, &c. ; amongst the latter are the genera Stimulus, 

 Dioicorca, Lonicera, Polygonum, &c. This winding in a particular 

 direction is not only confined to the species of a genus, but to the 

 genera of an order ; and Mohl, who has paid great attention to this 

 subject, states that he knows of but one exception to this rule, which 

 is the genus Abrus, in the order of LeguminosK, which twines to the 

 left, whilst all the others twine to the right. The direction of the 

 spires of the cirrhi is not so constant. Between the twining of the 

 cirrhi and the stems of plants Mohl has pointed out an essential 

 difference. The cirrhi are first developed longitudinally, and the spiral 

 tendency proceeds from the point to the base ; but in stems the first 

 three or four internodes grow straight, and the next internode is 

 developed very rapidly; and from this lower internode the spiral 

 tendency is developed upwards. Sometimes a spiral direction is seen 

 in the direction of trees that ordinarily grow straight ; and Gothe 

 records several instances of twisted trunks in the chestnut, the white- 

 thorn, beech, and others. A remarkable instance of spiral structure 

 connected with function is seen in the peduncle of the female flowers 

 of Valieneria, which is a water-plant. The female flowers spring to 

 the surface of the water in the summer, at the time the male flowers 

 have perfected their pollen, and scattered it upon the surface of the 

 water. As soon as the pollen is conveyed to the female flower its 

 spiral stem becomes contracted, and its fruit is perfected at the bottom 

 of the water. 



The most remarkable and important exhibition, in a practical point 

 of view, of the spiral tendency in plants, is the arrangement of the 

 leaves upon the axis of the plant. If we take a branch of the willow, 

 oak, pear, apple, or many others, and examine the leaves, we shall 

 find they are arranged in such a manner, that if we were to draw a, 

 line from leaf to leaf up the stem, we should produce upon it a spiral 

 which would in the case of any of these trees be of a different character 

 from any of the others. In theoretical botany the spiral arrangement 

 of the leaves which makes them alternate upon the stem is looked 

 upon as their normal form, and those leaves which are opposite or 

 verticillate are supposed to be produced by the suppression of an 

 internodium. The spiral arrangement of the leaves on the stem has 

 been mode a matter of mathematical investigation by Braun and 

 Schimper, and it is found that this arrangement is possessed of certain 

 fixed mathematical properties. Of course the same observations are 

 applicable to all those parts of the plant, as the bracts, sepals, petals, 

 scales of the fruit, &c., which are considered modifications of the leaf. 

 The fruit of the common pine may be taken as an illustration of these 

 properties. If the cone of a pine or a spruce-fir be broken through 

 the middle, three scales will be observed, " which, at first sight, appear 

 to be upon the same plane ; but a more attentive examination shows 

 that they really originate at different heights, and moreover that they 

 are not placed at equal distances from each other ; so that we cannot 

 consider them as n whorl, but only a portion of a very close spiral. 

 But considering the external surface of the cone viewed as a whole, 

 we find that the scales are disposed in oblique lines, which may bo 

 studied 1, as to their composition, or the number of scales requisite 

 to form one complete turn of the spire ; 2, as to their inclination, or 

 the angle, more or less open, which they form with their axis ; 3, as 

 to their total number, and their arrangement round the common axis, 

 which constitutes their co-ordination. Finally, wo may endeavour to 

 ascertain whether the spires turn from right to loft, or vice versa." 

 (Liudley.) 



In the arrangement of the leaves several series of spires are dis- 

 coverable, and between these there constantly exists a certain arith- 



