46 SEVENTH REPORT. 



These investigation, as far as tliey go, point towards tlie conclusion 

 that the stimulative influences upon plants, produced by the several 

 parts of the solar spectrum, can not be predicted. Experimental evi- 

 dence is required in each function, and with each part of the spectrum. 

 The published conclusions of almost all investigators on this particu- 

 lar question, seem to have been influenced, more or less, by the purely 

 chemical efl'ects of the several parts of the spectrum. The rays of 

 greatest, refrangibility have, almost without exception, the greatest 

 chemical activity; but in phj-siological functions there is a great variety. 

 This alone would seem to indicate that vital activities are not purely 

 chemical actions; or, that there are numbers of chemical actions, differ- 

 ing from those at present known, yet undiscovered. 



Plants have by nature been accustomed to sunlight, and it Avould 

 seem as though they have been subjected to this stimulus, not divided 

 up into its parts as they are in the solar spectrum, but as white light. 

 Therefore, it seems also apparent that the ecological effects of the indi- 

 vidual colors would be of little importance. Such, however, in a vast 

 number of cases, is not the condition, when we consider that it is the 

 nucleus and the cytoplasm within the cell, that have fundamentally to 

 do with vital activity of all kinds. To reach this nucleus and cyto- 

 plasm, the light has to pass through, in most cases, cell-walls and other 

 refractive bodies, and therefore would be, more or less, a spectrum when 

 acting upon the protoplasm (cytoplasm and nucleus). In the case of 

 such plants as have collench^^ma tissue within the stems, it is quite easy 

 to see that these prisms of cellulose would be perfectly adapted to pro- 

 duce a spectrum within the tissue. Take the case of crystals, oil globules, 

 starch grains, and a host of other refractive bodies; it is quite clear, 

 therefore, that spectra would be produced within the living cells in a large 

 number of instances. 



And, if it be considered that the light has to pass through a consid- 

 erable amount of matter before reaching the protoplasm, we can see 

 that some parts of the light may be absorbed in the process of pene- 

 tration. The light stimulus would be, in such cases, not that of white 

 light, but that of some one color, or a combination of colors with one 

 or more lacking. All aquatic plants are subjected to light which has 

 not the full spectrum of sunlight, owing to the fact that the light has 

 to pass through water, and this more or less impure, to reach the plant. 

 And further, this modified light will again be affected in passing through 

 the cell-walls and cell-contents in its course towards the protoplasm. 



Another special instance should be mentioned. In all aerial (laud) 

 plants, there are intercellular sipaces which are filled with air. These 

 spaces are of a multitude of forms and sizes; and they are usually 

 located — especially in the leaves — adjoining, or near, the living active 

 cells. These intercellular spaces, then, are so many air bubbles among 

 the cells, and it needs no argument to convince any one who has used 

 a microscope, that these air bubbles have a high refractive power for 

 light. In fact the tender white stem of a young seedling owes its white- 

 ness to the fact that it has a large number of prismatic intercellular 

 spaces all filled with air. Even the unicellular plant would be influenced 

 by the refraction produced by its wall and cell content ; the mycelium 

 of fungi are so many transparent cylindrical prisms of high refractive 

 power, as compared with air. So that when we speak of the stimulus 



