SPECIFIC "ENERGY OF ASSIMILATION. 313 



that function. Hence repeated measurements of the leaves must accompany 

 the growth of the plant — an exceedingly troublesome task. We may of course 

 also proceed by preventing a plant, already provided with a large assimilating 

 surface, from increasing the latter and using up its products of assimilation in 

 the shoots, which develope in the dark and thus take no part in assimilation. 

 But even here many difficulties arise. According to the first method, Weber 

 found that in four species of plants distinguished by their thin and relatively large 

 leaves, and by their rapid growth and considerable increase in weight in a short 

 time, a square metre of leaf-surface produces the following quantities of starch 

 in ten hours of daylight : — 



TropcEohim majus . . . . . . 4*446 grams. 



Phaseolus inultifloriis . . . . . . 3*2 15 „ 



Ricinus conwiwiis ...... 5*292 „ 



Helianthus amiuus ...... 5'559 „ 



It is to be remarked, however, that the ash contained in the dry substance should 

 be deducted from the calculation, and the loss of organic substance by respiration 

 added to it; since the increase in weight of a plant in organic substance is, as a 

 matter of fact, only the difference between the quantities gained by assimilation 

 and the quantities, of course much smaller, lost in respiration. This opportunity 

 may be taken for making the additional remark that the quantities of starch present 

 for the time being, which may be detected incidentally in the chlorophyll-corpuscles, 

 is only transitory, since the starch arising in the chlorophyll by assimilation 

 is continually being dissolved in the light, as well as in the dark, and conveyed 

 into other portions of the plant. During vigorous assimilation its accumulation 

 in the chlorophyll predominates : in continuous darkness, or feeble illumination, 

 on the other hand, the solution and translocation of the starch prevail, and it is 

 this which renders it possible to deprive the chlorophyll-corpuscles of starch for experi- 

 mental purposes. 



Weber's experiments were made, however, not in the open air but in a 

 greenhouse, the illumination of which was very strong, it is true, but still not normal, 

 as in the open. We may therefore assume that in the latter case the assimilation 

 would have been more energetic, and the more so since plants in the open can 

 also develope their roots more normally than in Weber's experiments, where they 

 were confined in pots. This supposition is to a certain extent confirmed by 

 Kreussler's measurements, which, to be sure, were made by very different and less 

 exact methods. Maize plants, according to these experiments, yielded as much as 

 seven grams of starch per square metre in ten hours, under the above conditions ; 

 and observations made later in my laborator}- on Gourd plants, rooted in the open, 

 yielded a probable number of eight grams of starch per square metre of leaf- 

 surface per day, which nevertheless would give in 100 days only 800 grams of dry 

 substance, while in a sunflower {Helianthus amtuus) I obtained in 100 days more 

 than 1400 grams of dry substance, although the foliage during the first fifty days 

 was certainly less than half a square metre, and even later did not amount to a 

 whole square metre. It is thus to be expected that the energy of assimilation 

 may, under certain circumstances, be considerably greater than eight grams per day 



