520 REPORT— 1880. 



the first six of the exclusion of the potass, there has been nearly 400 los. less carhou 

 assimilated per acre per annum ; and in some of the still later years the deficiency 

 has heen very much greater than this. 



We have here, then, the .significant fact that an equal amount of nitrogen wa.s 

 taken up in both cases, that chlorophyll was abundantly produced, but that the full 

 amount of carbon was not assimilated. In other words, the nitrogen was there, the 

 chlorophyll was there, there was the same sun-light for both plots ; but the assimi- 

 lation-work was not done where there was not a due supply of potass. 



Again, in the field in which barley has now been grown for twenty-nine years 

 in succession, there are two plots which have annually received the same amount of 

 nitrogen — the one in conjunction with salts of potass, soda, and magnesia ; and the 

 other with the same, and superphosphate of lime in addition. The plot without 

 the superphosphate of lime alwaj's maintains a darker green colour. At any given 

 period of growth the dry substance of the produce would undoubtedly contain a 

 higher percentage of nitrogen ; but there has been a deficient assimilation of carbon, 

 amounting to more than 500 lbs. per acre per annum, over a period of twenty-eight 

 years. Here again, then, the nitrogen was there, the chlorophyll was there, the 

 sun-light was there, but the work was not done. 



It may be stated generally that, in comparable cases, depth of green colour, if 

 not beyond a certain hmit, may be taken to indicate corresponding acti'N'ity of carbon 

 assimilation ; but the two instances cited are sufticient to show that we may, so far 

 as the nitrogen, the chlorophyll, and the light are concerned, have the necessary 

 conditions for full assimilation, but not corresponding actual assimilation. 



It cannot, I think, fail to be recognised that in these considerations we have 

 opened up to view a very wide field of research, and some of the points involved 

 we may hope will receive elucidation from the further prosecution of Dr. Siemens's 

 experiments. He will himself, I am sure, be the first to admit that what he has 

 already accomplished has done more in raising than in settling important questions. 

 I understand that he proposes to submit plants to the action of the separated rays 

 of his artificial light, and the results obtained cannot fail to be of much interest. 

 But it is obvious that the investigation should now pass from its present initiati\e 

 character to that of a strictly quantitative inquiry. 'We ought to know not only 

 that, under given conditions as to light, plants acquire a deeper green colour and 

 attain maturity much earlier than under others, but how much matter is assimi- 

 lated in each case, and sometliing also of the comparative chemical characters of 

 the products. As between the action of one description of light and another, and 

 as between the greater or less continuity of exposure, we ought to be able to form a 

 judgment whether the proper balance between assimilation on the one hand, and 

 growth and proper maturation on the other, has been attained ; whether the 

 plants have taken up nitrogen and mineral matter, and produced chlorophyll, in a 

 greater degree than the quantity and the quality of the light have been able to 

 turn to account ; or Avhether the conditions as to light have been such that the 

 processes of transformation and growth from the reserve material provided by 

 assimilation have not been normal, or have not kept pace with the production of 

 that material. 



But one word more in reference to Dr. Siemens's results and proposed extension 

 of his inquiries. Even supposing that by submitting growing crops to continuous 

 light by the aid of the electric light during the night, they could be brought to 

 maturity within a period shorter than at present approximately in proportion tn 

 the increased number of hours of exposure, the estimates of the cost of illuminating 

 the vegetation of an acre of land certainly do not seem to hold out any hope that 

 agriculture is likely to derive benefit frcun sucli an application of science to its 

 needs. If, however, the characters of growth and of maturation should prove to 

 be suitable for the requirements of horticultural products of luxury and high value, 

 it may possibly be otherwise with such productions. 



The above considerations obviously suggest tlie question : "What is the office of 

 chlorophyll in the processes of vegetation ? Is it, as has generally been assumed, 

 confined to effecting, in some way not yet clearly understood, carbon assimilation, 

 and, this done, its function ended ? Or is it, as Pringsheim has recently suggested-,, 



