STRUCTURE.] COLOUR DEVELOPMENT. 47 



through them of the Rotifer vulgaris, and of minute granular 

 matter. He considers the openings intended " to guarantee 

 the organs of respiration from the too great influence of the 

 air." But I do not perceive in what way such an effect is to 

 be accomplished. Similar openings are found at the point of 

 contact of the ends of spiral, and other vessels, or tubes. 



With reference to this subject, it may be observed, that the 

 bladders of cellular tissue often contain air-bubbles, which 

 appear to have no direct means of escape, and that the limits 

 of colour are always very accurately defined in petals, as, for 

 instance, in the stripes of tulips and carnations, which could 

 not be the case if cellular tissue were perforated by such 

 holes as have been described ; for in that case colours would 

 necessarily run together. 



Cellular tissue is generally transparent and colourless, or 

 at most only slightly tinged with green. (See page 10). The 

 brilliant colours of vegetable matter the white, blue, yellow, 

 and scarlet hues of the corolla, and the green of the bark and 

 leaves is not owing to any difference in the colour of the 

 cells themselves, but to colouring matter of different kinds 

 which they contain. In the stem of the Garden Balsam 

 (Impatiens Balsamina), a single cell is frequently red in the 

 midst of others that are colourless. Examine the red bladder, 

 and you will find it filled with a colouring matter of which 

 the rest are destitute. The bright satiny appearance of many 

 richly coloured flowers depends upon the colourless quality of 

 the tissue. Thus, in Thysanotus fascicularis, the flowers of 

 which are of a deep brilliant violet, with a remarkable satiny 

 lustre, that appearance will be found to arise from each 

 particular cell containing a single drop of coloured fluid, 

 which gleams through the white shining membrane of the 

 tissue, and produces the flickering lustre that is perceived. 

 [The cause of colour in plants will be spoken of hereafter in 

 the second book.] 



The bladders of cellular tissue develope, in some cases, with 

 great rapidity. I have seen Lupinus polyphyllus grow in 

 length at the rate of an inch and a half a day. The leaf of 

 Urania speciosa has been found by Mulder to lengthen at the 

 rate of from one and a half to three and a half lines per hour, 



