HARD WICKE* S S CIENCE- G OS SI P. 



171 



increased. This diminishes the turgescence of the 

 cells of the exposed sides, the cell walls of which 

 contract in consequence, and the whole organ is re- 

 flexed. It is also probable that some of the water 

 passes from the exterior side to the intercellular 

 spaces of the interior one, which is hence rendered 

 more turgid and forces the other back. Under these 

 circumstances the inner side would be in a state of 

 active tension, and the outer of passive. These con- 

 ditions continue during the expbsure to direct sun- 

 light, but when dense clouds intervene, or darkness 

 comes on, the phenomena are reversed. Temperature 

 is diminished, transpiration decreases, the cells of the 

 exterior become turgescent, probably by the trans- 

 ference of water from the cells of the interior side, 

 and consequently the length of the exterior portion 

 is increased, whilst that of the inner is proportionally 

 diminished. Or in other words the exterior sides are 

 in a state of active tension, and the inner of 

 passive. 



Coincidentally with the processes that are going 

 on in the green involucral bracts, the ray florets are 

 being acted upon by the sun's rays. These cause 

 them to expand their internal surfaces so as to reflect 

 the greatest possible amount of sunlight and thus 

 render the flowers conspicuous. In this way they are 

 more readily distinguished by the insects who seek 

 food in the tiny florets, and who are thus the uncon- 

 scious agents of fertilisation. But how it is that the 

 sunlight causes the ray florets thus to expand them- 

 selves is not easy to determine, or at least a ready 

 solution is not present to the mind of the writer. 

 Possibly it is a power inherited from the true foliar 

 organs, from which they have been modified, as 

 leaves possess the power of expanding their lamina 

 so as to catch the greatest possible amount of sun- 

 light. This is very conspicuous in the rosette of 

 radical leaves of the daisy, in which the arrange- 

 ment is a compressed spiral. The thought also 

 suggests itself that this compressed spiral of radical 

 leaves is repeated in both the involucre and the 

 capitulum. In the case of true foliar organs, this 

 power of exposing their broadest surfaces to the sun 

 is for the purpose of assimilation, whereas when they 

 are modified into floral organs it is to render them 

 attractive to insects. It is also noteworthy that in 

 the latter case they no longer assimilate, but con- 

 sume, for their tissues are constructed from the 

 materials elaborated by the true leaves and other 

 green organs. 



In the closing of the ray florets when no longer 

 stimulated by direct sunlight, they are probably 

 passive to the force exerted by the closing of the 

 surrounding bracts. They are also doubtless affected 

 by the diminution of light. 



The movements induced both of the ray florets 

 and the involucral bracts are not uniform through 

 their whole length, but are most active in a zone 

 near the base of the bracts and just above the tube of 



/ 



the ray florets. "Whether these movements are ac- 

 companied by growth in length, or otherwise, would 

 require careful observation to determine, but the in- 

 crease in length, if any, would be exceedingly small, 

 and could only be expressed micrometrically. Such 

 growth is possible, and its probability is suggested 

 by the fact that it is always preceded by turgescence 

 of the cells. To the phenomena of unequal growth of 

 the sides of bilateral organs, the term Nutation is 

 applied. 



In all these complicated movements the real agent 

 is the protoplasm of the living cells. It is this which 

 has the power of imbibing water and also of parting 

 with it into the adjacent intercellular spaces. These 

 movements of the water contained by the protoplasm 

 are accompanied by the exertion of considerable 

 force. This force is converted by the elasticity of 

 the cell walls into motion, which affects the whole 

 organ. The elastic cell walls are passive to the 

 energy of the protoplasm which they enclose, and 

 from which they were originally formed. This is the 

 only living thing in the plant, and it is this which is 

 sensitive to external stimuli, such as light and heat. 

 It cannot be too strongly maintained that the proto- 

 plasm is the essentially vital principle in all plants. 

 In its substance the whole of the materials from which 

 their tissues are constructed was originally formed, 

 and by its energy their various organs have been 

 differentiated. 



J. Saunders. 



Luton. 



THE ELECTRIC LIGHT APPLIED TO THE 

 MICROSCOPE. 



IN the part of the Journal of the Royal Micro- 

 scopical Society for February last is an article by 

 Mr. Steam, the inventor, on a Special Microscopical 

 Swan Incandescent Electric Lamp. As I have 

 bought one, perhaps my experience of it may be 

 interesting to some readers of this paper. The lamps 

 are miniatures of Swan's, being with the battery, &c, 

 made by Mawson & Swan, of Newcastle-on-Tyne. 

 Each lamp consists of a glass globe T 7 g in. diameter, 

 in which is a carbon filament T g in. long and ygg in. 

 diameter. At the bottom of the globe the glass is 

 fitted into an ebonite socket about % in. high, on each 

 side of which is a strip of brass for connecting with 

 the wires from the battery. The lamp weighs about 

 I ounce, and costs \os. 6d. The battery consists of 

 five large special new form Leclanche cells in a 

 wooden box, price 37^. complete. These, with is. 

 worth of covered wire, are the only essential 

 things. Any other battery sufficiently powerful 

 will do, if the fumes are not objectionable. Each 

 Leclanche cell would, when empty, hold about three 

 pints. Each contains a central column with six 

 grooves, surrounded by six thick circular pencils of 



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