CHEMISTRY. 



93 



ence of the ferment from the flower to the 

 fruit remained to be accounted for. Thinking 

 it might be due to the agency of insects, M. 

 Bontroux examined the bees which frequented 

 flowers in the nectar of which he had found 

 the ferment-plants, and found the same kinds 

 upon them. M. Bontroux explains the life- 

 history of these organisms as follows: The 

 ferments developed in flowers and fruits dur- 

 ing the summer are preserved during the cold 

 season, partly, perhaps, in the remains of plants, 

 partly in the ground, and partly in the winter 

 habitations of insects. In the spring, the germs 

 that remain alive are borne by insects to the 

 nectariferous flowers, where they are devel- 

 oped; in summer they are cultivated from 

 flower to flower, being sown from one to an- 

 other by insects that visit them, and are car- 

 ried to ripe fruits by the same agency. 



It has been in dispute whether plants absorb 

 noxious substances which may be present in 

 the soil, or have a capacity to discriminate 

 against them. Freytag concluded, from ex- 

 periments he made, that they have no discrim- 

 inating power, but are compelled to take up 

 whatever may be in the soil in a suitable form 

 for assimilation. Liebig lias advanced the same 

 doctrine, but it has been contradicted by the 

 results of experiments made by other observ- 

 ers. Mr. Francis 0. Phillips publishes, in the 

 "Journal of the Franklin Institute," the re- 

 sults of experiments which he made on this 

 subject with selected plants, at Alleghany Park. 

 His conclusions are, that healthy plants, grown 

 under favorable circumstances, may absorb 

 through their roots small quantities of lead, 

 zinc, copper, and arsenic; that lead and zinc 

 may enter the tissues in this way without 

 causing any disturbance in the growth, nutri- 

 tion, and functions of the plant, and that the 

 compounds of copper and arsenic exert a dis- 

 tinctly poisonous influence, tending, when pres- 

 ent in large quantity, to check the formation 

 of roots, and either killing the plant or so far 

 reducing its vitality as to interfere with nutri- 

 tion and growth. Freytag and others have 

 supposed that the absorption of poisonous met- 

 als causes no disturbance until a certain degree 

 of concentration is reached, when the plant 

 rapidly withers and dies; while others sup- 

 pose that the plants absorb no such substances. 

 The theory of Freytag seems to have the 

 weight of facts in its favor, and if it is possible 

 that crops may become charged in this way 

 with poisonous elements of the soil, it becomes 

 a matter of the highest importance that, wher- 

 ever there is danger of such impregnation, the 

 most efficient means be employed for avert- 

 ing it, for soil once impregnated with copper, 

 lead, and zinc, may year after year bear crops 

 poisoned in the same manner. 



Ad. Mayer has reinvestigated the question 

 of the capacity of the leaves of plants to as- 

 similate ammonia. He found it to exist in 

 the higher plants, but that the legumes, which 

 are believed to gather considerable quantities 



of nitrogen from the air, have no peculiar 

 power in this respect. He infers that the prac- 

 tical significance of the capacity is very small. 

 Experiments by Hasselbarth and Wein indi- 

 cate that while nitrates are readily assimilated 

 by plants, ammonia is taken up with difficulty, 

 if at all. 



The most noticeable recent experiments on 

 the sources of the ash ingredients of plants are 

 those of Grandeau on the functions of the so- 

 called mature noire of fertile soils, or the black 

 inorganic matter, insoluble in water or acids, 

 but soluble in alkalies, which can be extracted 

 from the soil by ammonia. Notwithstanding 

 it has been made probable that the organic 

 matter in the soil does not contribute directly, 

 to any appreciable extent, to growth of the 

 plant, those soils which are distinguished for 

 their fertility in general contain much humus, 

 and soils deficient in organic matter are usual- 

 ly improved by adding humus to them. Gran- 

 deau believes that the organic matter contrib- 

 utes to this property by acting as a solvent 

 by means of which the inorganic salts in the 

 soil are embodied in a peculiar compound with 

 it, and are thus taken up and supplied to the 

 roots of the plant in an assimilable shape, and 

 has published the results of a number of ex- 

 periments made by him with the matiere noire 

 of the Kussian " black earth " and with other 

 soils, in support of his view. Professor H. P. 

 Armsby suggests that the humus acts through 

 its decomposition, by supplying carbonic acid 

 as a solvent for the rock-dust with which it is 

 intermixed. Hence, if by any means the or- 

 ganic matter in the soil be increased, especial- 

 ly if it be finely divided and uniformly distrib- 

 uted, we have a considerable increase in the 

 carbonic acid of the soil, and an increase in 

 the rapidity of the solvent action which con- 

 verts rock-dust into available plant-food. Add 

 to this the solvent action of the acids formed 

 by the decay of the organic matter, and the 

 effect on the porosity, temperature, permeabil- 

 ity, etc., of the soil, each in its. turn reacting 

 on the rate of weathering as well as on the 

 growth of the crop, and we can readily see 

 why humus should have a high value in the 

 soil. Moreover, the natural organic matter of 

 the soil is a consequence as well as a cause of 

 fertility. A large amount of humus in a soil 

 implies an abundant previous growth of vegeta- 

 tion, and this in its turn implies a soil of at 

 least moderate original fertility. 



It is agreed that the greater part of the car- 

 bon in plants is derived from the carbonic acid 

 of the air ; but the question has been much 

 discussed whether a part of it may not be de- 

 rived directly from the carbon matters con- 

 tained in fertile soils. A few experiments by 

 Van Tieghem and Blociszewski in the growth 

 of embryos deprived of their endosperm in arti- 

 ficially-supplied albumen apparently confirmed 

 the view that it might. Other experiments by 

 Stutzer, in which it appeared that no growth 

 took place when carboxyls only were present, 



