26 AXATOiJY OF THE LEAF. 



cells of the Leaf, it will readily be admitted that^ since the cellular structure 

 of the organ is colourless and diaphanous^ the green colour of leaves generally 

 must depend upon the presence of this granular material. Such is actually 

 the case, although at first it might not seem probable. 



But it now may be asked, upon what does a difference of colour of the 

 leaves or any other part of a plant depenil ? This is an interesting question, 

 but we cannot now fully enter upon it; let it suffice me to state, generally, 

 that the granular matter is either red, blue, green, or violet, according as, in the 

 one case, it is disposed to reflect, or has an apjx'fite for reflecting the red, or 

 least refrangible rays; or, as in the other instance, it reflects either the violet, 

 or most refrangible rays; or any of the other intermediate rays, of which a 

 beam of solar light is constituted. In what, however, this inherent property 

 of absorbing or decomposing light consists, we cannot at present determine; 

 therefore, without entering any further into the ''Theory of Colours," we shall 

 at once return to what we were discussing respecting the contents of the 

 vesicles or cells. 



Beside granules every true cell contains, at some period or other, a small 

 oval or round bo:ly, called a nucleus. This nucleus is usually regarded as 

 the centre from which the cell originated; but there are numerous theories 

 as to the mode in which cells spring up and are developed; and the subject 

 of cell development, or Cytogenesis, being of extreme intricacy and delicacy, 

 to enter further upon this subject would be altogether foreign to our pur- 

 pose. I cannot waive it^ however, without remarking by the way that 

 there seems to exist in the human mind an insatiable desire to unravel 

 Nature's greatest mystery. It is this that has unhappily led many of our 

 most enlightened philosophers to start aside from the truth once revealed, to 

 place their faith only in the vague notion, ''That organized bodies, whether 

 simple, compound, or complicated, are all of spontaneous origin." Thus fatally 

 overlooking the first, the great, the eternal cause! 



But to return. Beside the nucleus, wc often find a quantity of Crystals, 

 or Eaphides, These bodies viewed under the micrascope have frequently the 

 appearance of bundles of fine needles. They are very numerous in the leaf- 

 stalk of the Rhubarb, in which plant they exist as oxalate of Lime. Starch 

 grains are also found, but these occur more fie(juent]y in the cells of the 

 root and fruit, as in the Potatoe and Wheat. 



There is one other deposit to which I shall briefly allude, that is called 

 Lignine, or Woody Matter. This substance is that which gives to the veins 

 or ribs of the leaf a tough and fibrous character, aud in its more highly- 

 developed condition it constitutes ordinary wood; while in the seeds of many 

 foreign Trees, such as the Ivory Palm for example, it assumes an almost 

 stony hardness. 



I have now to say a few words about the vessels of the leaves. Vessels 

 are elongated cells placed end to end, which sometimes communicate with each 

 other, forming complete hollow tubas; at other times they are closed. Their 



