64 



SCIENCE-GOSSIP. 



v.'ork is carried out, depending only on the fire in 

 the furnace and the vrater in the boiler. Living 

 things, however, are marked off from all other 

 objects in Nature by the remarkable power of self- 

 adjustment they possess. 



For instance, we have already seen that light is 

 an essential factor in the nutrition of plants. Rays 

 of a certain intensity must fall upon the green 

 grains of the leaf: but if too much light were to 

 meet ihem, their delicate mechanism would be 

 overstrained and irreparable ruptures would take 

 place. In li\"ing plants, howe%-er, these dangers 

 are ob%-iated by the wonderful changes that take 

 place in the arrangement of the parts of the leaf in 

 accordance with the quantity of Hght which falls 

 upon them. If we examine a leaf microscopically 

 we shall see that it is built up of a large number of 

 infinitely small boxes or "cells" piled up side by 

 side and one over the other, to give the leaf its 

 outwcird shape. Each of these cells contains some 

 of the green chlorophyll grains which we have 

 already learnt to know. If now a leaf be exa mi ned 

 which has been exposed to only moderate iUnmina.- 

 tion, it wiU be found that the chlorophyll grains 

 are all arranged upon the upper and lower surfaces 

 of the cells, so that all the light which falls upon 

 the leaf wotild directly meet them. If the same 

 plant be then exposed to bright sunlight and 

 another leaf examined, it will be noticed that the 

 green grains have all travelled away from the 

 upper and lower surfaces and are now drawn up 

 along the side walls of the cells, so that only a 

 Tninimum of light can fall upon them, and they are 

 protected from the harmful effects of a too intense 

 illu m ination. This is only one of many changes 

 that are effected in the plant body by alterations 

 in the degree of hght. 



Again, another remarkable adaptation to circiun- 

 stances is shown by the tendrils of cUmbing-plants. 

 It is the duty of these structures to cHng to rigid 

 supports, and so raise the slender stem of the 

 climber high up into the air and hght. If you 

 carefully watch a tendril — for instance that of 

 Tacsonia — you will see a strange phenomenon 

 taking place tmder your eyes. As the tendril grows 

 out from the stem, it continually sweeps round and 

 round in an ever- widening circle, seeking as it were 

 with blind eyes for some support to which it can 

 chng, groping like a man in the dark for something 

 to gtiide its progress. " It was an interesting 

 spectacle " says Charles Darwin, in his work on 

 " CUmbing Plants," " to see the long tendril sweep- 

 ing this grand circle, night and day, in search of 

 some object round which to twine.' 



With regard to the cause of this movement, I 

 need only say that it is due to the unequal growth 

 of the different sides of the tendril, so that its apex 

 points to each direction of the compass in turn. 

 If such a tendril be gently pressed or rubbed at any 



point, it at once evinces its sensitiveness to contact 

 by bending vigorously and rapidly at the point 

 which was touched. In nature the same thing 

 occurs : as the tendril revolves it will, under favour- 

 able circumstances, meet with some external object, 

 such as a branch or piece of stick, which by reason 

 of its mere contact causes the tendril to bend at the 

 point of meeting, and so gradually to wind itself 

 round the object. 



These two examples must suffice to illustrate the 

 manifold and strange phenomena of sensitiveness 

 or irritability in plants. Everyone is acquainted with 

 that other example of a plant sensitive to contact or 

 touch, the famous sensitive plant. Mimosa pudica, 

 which has been referred to by botanists till we are 

 almost weary of its name, which is so dear to the 

 hearts of the unscientific and which has been 

 immortalised in the noble verses of a great English 

 poet. Perhaps less familiar, but no less truly 

 present, is the power of adaptation possessed by 

 Uving plants to changes of temperature, to the 

 direction of the force of gTa\"it\- and to the other 

 forces of nature ; but beyond these references space 

 will not permit me to go. 



To complete our picture of a Uving plant, some 

 account should here be given of the processes of 

 reproduction by which the plant, after its own 

 death, can yet continue to produce its kind. This 

 subject, howe%-er, would take us far into the 

 theories and facts of microscopical science. "We 

 must be content, therefore, with a brief statement 

 of some of the more obvious points which can be 

 seen with the naked ej-e. A flower, as I need 

 hardly tell you, consists, from without, inwards of 

 sepals, of petals, of stamens and of a pistil. The 

 stamens are packed with small grains of pollen and 

 within the pistil lies the germ of a future seed, 

 which, however, cannot develop unless poUen, 

 preferably from another flower, has first fallen 

 upon the pistil. We may well ask how is it that 

 the poUen from the stamens of one flower is brought 

 to the pistil of another ? Thanks, more particularly, 

 to the work of our great countrjnnan, Charles 

 Darwin, we can almost completeh- answer this 

 question. It was fotmd that the most important 

 agents in this tranference of pollen are the wind 

 and insects. 



In the springtime, clouds of poUen are swept up 

 by the wind from the pine-trees or from the willows, 

 and some of this immense quantity must almost 

 inevitably be borne to the pistils of other flowers. 

 When the pines are in bloom, almost everything 

 indoors and out, even far from their neighbourhood, 

 becomes dusted over '.vith some of the pollen, and 

 the appearance is spoken of as " sulphur rain." 



Far more potent, however, than the wind, are 

 uisects : the bee buzzing from blossom to blossom 

 has time after time been seen, with its hairy body, 

 to transfer the poUen from stamen to pistil, and 



