CHAMBERS'S INFORMATION FOR THE PEOPLE. 



It is true that the leaves elongate, the flowers 

 expand, the anthers burst, and the seed-vessels 

 open spontaneously ; but these are movements 

 caused by the progressive development of the 

 plant, and subjected to regular laws. The sponta- 

 neous movements to which reference is now made 

 are quite different as, for example, those of the 

 leaves of Hedysarum gyrans. This plant has 

 compound leaves, the terminal leaflet of which 

 displays a slight oscillatory motion ; but the side- 

 leaflets have such eccentric movements, as to ren- 

 der it difficult, if not impossible to explain them, 

 and which might appear, indeed, to a fanciful 

 mind as though the whole plant were actuated by 

 a feeling of caprice. Generally, all the leaflets 

 twist and whirl themselves about in an extra- 

 ordinary manner, though the air of the hot-house 

 in which they grow is perfectly still ; but frequently 

 the leaflets on only one side will be affected, and 

 sometimes only a single leaflet will move, or all 

 will become motionless together ; and when this 

 is the case, it is quite in vain to attempt to set 

 them again in motion by touching them ; though 

 sometimes in a moment, after the touching has 

 ceased, the leaflets will begin to move again as 

 rapidly as before. In like manner, the side-leaflets 

 frequently continue their movements all night, 

 while the terminal leaflet remains quietly folded 

 up. Cold stops the motion of the leaves, which 

 begins again so soon as the heat of the stove in 

 which the plant grows is renewed. 



Plants may be deprived of their irritability by 

 the vapour of prussic acid, chloroform, or ether. 



Colour. The colours of plants present many 

 points of interest for the consideration of the 

 student, and are connected with many important 

 phenomena in vegetation. It is to colour, perhaps, 

 more than to form, that vegetation, as a whole, 

 often owes its importance in the landscape. The 

 gay colours of plants usually reside in the corolla, 

 the leaves being usually some shade of green ; but 

 in the case of sea-weeds and other cryptogams, 

 the whole plant is often of a bright red, or green, 

 or olive, according to the species, a character 

 which has afforded the basis of the classification 

 of sea-weeds now in use. 



The green colour of leaves and the gay colour 

 of flowers depend upon different kinds of colour- 

 ing-matter contained in the cells of the plant, for 

 the cell-walls are without colour themselves. In 

 the green parts of plants, this colouring-matter is 

 in the form of microscopically minute green 

 granules of chlorophyll, which are only produced 

 under the action of light ; hence plants grown in 

 the dark are etiolated. The changes which it 

 undergoes, according to its state of oxidation, 

 explain the tints which green leaves acquire in 

 autumn. The yellow leaves of autumn contain 

 proportionately more wax than the green leaves of 

 summer, and the yellow rind of ripe fruits more 

 than the green rind of unripe fruits. 



The colours of parts not green are due to a 

 different kind of colouring-matter, termed chromule, 

 whose chemical relations to chlorophyll have not 

 been fully investigated. Chromule is usually dif- 

 fused throughout the sap of the cells ; as in the 

 flower of the tulip, for example, a strip of the 

 epidermal tissue of which will shew well, under 

 a common compound microscope, the beautiful 

 arrangement of cells of different colours, so as to 

 give the general effect seen in this gaudily painted 



78 



flower. In some cases, however, chromule is found 

 in the form of distinct granules. The colours of 

 flowers are arranged in two series the cyanic or 

 blue, and the xanthic or yellow. A species belong- 

 ing to the blue series may exhibit all shades of 

 white, purple, and violet, but will not become yellow ; 

 and one belonging to the yellow series may exhibit 

 all shades of white and orange, but will not become 

 pure blue. Both series unite in red. Although 

 light is essential to the development of the green 

 colour of leaves, its immediate action is not always 

 required for the development of the chromule of 

 flowers a fact quite in accordance with the 

 practice of florists, who keep their favourite dahlia 

 and pansy blooms covered up in their later 

 stages. In accordance with this, also, is the 

 fact, that flowers grown in the shade are seldom 

 different in colour from those fully exposed to the 

 air and light. Flowers may be made to change 

 their colours by the influence of the soil in a 

 most remarkable manner. The petals of the 

 common hydrangea, which are naturally pink, 

 are said to be made blue by planting the shrub 

 in soil impregnated with iron, or providing it 

 with charcoal. The change produced in tulips, 

 carnations, heart's-eaces, &c. is still more extra- 

 ordinary. The flower of a seedling tulip is gener- 

 ally uniform ; and after remaining of this colour 

 two or three seasons, it will suddenly break, as the 

 florists term it, into the most brilliant and varied 

 tints of rose, white, yellow, brown, or purple, with- 

 out leaving any trace of the original colour. To 

 produce this change, florists try a variety of 

 means, all of which have relation to the soil ; for 

 example, they sometimes keep their tulips in poor 

 soil, and then suddenly transplant them into one 

 exceedingly rich ; or they reverse the process : at 

 other times they change them suddenly from a 

 sandy to a clayey soil. Even the chlorophyll of 

 plants is often developed under circumstances 

 where the influence of light is very slight, and 

 would appear to depend in some measure upon 

 other agents. Ferns and mosses have been found 

 green in mines where they have grown in almost 

 total darkness ; and green and red sea-weeds of 

 the most brilliant tints grow at great depths in the 

 ocean, where the light, being weakened by passing 

 through such an immense body of water, can have 

 but little colouring effect 



Although it has been stated by Ruskin that 'the 

 natural colour of objects never follows form, but is 

 arranged on a different system,' the investigations 

 of Professor Dickie on the relations between 

 colour and form in plants seem to indicate a 

 different result. He finds I. That in polypetalous 

 and gamopetalous flowers, of regular form such 

 as the primrose, gentian, and pimpernel the dis- 

 tribution of colour is uniform on the different 

 petals, whether free or in cohesion, whatever be 

 the number of colours present ; 2. That flowers 

 whose form is irregular as, for example, papili- 

 onaceous flowers, where certain petals are larger 

 than the others present an equally irregular dis- 

 tribution of colour, whether one or more colours 

 be present ; 3. That different forms of corolla, in 

 the same head of flowers, often present differences 

 of colour ; but all of the same form agree also in 

 colour. 



Fragrance. The cause of fragrance in flowers 

 has never yet been fully explained. All organ- 

 ised bodies consist partly of volatile matters, 



