68 



Garden and Forest. 



[February 6, 1889. 



plants do best in baskets filled with sphagnum and large lumps 

 of charcoal in the warmest house, with abundance of water 

 at all seasons, not allowing them to become dry at anytime. 

 Kenwood, N.Y. F. Goldring. 



Propagation of Daphne Cneorum. — This beautiful shrub has 

 always been comparatively scarce, on account of its slow and 

 somewhat difficult propagation by ordinary methods. To 

 multiply it rapidly the following method has been successfully 

 practiced : remove two or three inches of the soil about and 

 among some strong plants, in open ground, in spring, and 

 fill in carefully with very fine compost, almost to the tops of 

 the branches, leaving, perhaps, two inches of their tips above 

 the surface. This will necessitate, also, careful pegging down 

 of the plants. 



The next spring, just as soon as the frost is out, remove with 

 the nicest care the compost, using a hose or a pail of water to 

 wash away the soil from the thickest part of the bush, and 

 there will be found multitudes of little white buds on the 

 branches, each standing out from the surface of the bark like 

 an excrescence, only held to the parent plant by a minute 

 thread, and each bud supplied with a straight, white root, the 

 whole looking like a seed of Clover when well sprouted, but 

 still below the surface. This Daphne has a great many leaves 

 on its branches, and in the axil of each one is a dormant 

 bud. These minute buds rarely develop under ordinary cir- 

 cumstances ; but the generous diet prescribed above causes 

 many of them to push, in their cool and dark situation, into 

 the shape described. 



These miniature plants come to the surface and develop 

 into strong and really independent plants, wherever they hap- 

 pen to receive enough light and space to encourage them. 

 But the greater part would be smothered by the shade or 

 crowded out, if unassisted. All that remains to do is to detach 

 them carefully from their native stem, which the least touch of 

 a fine point will accomplish, and plant them immediately in a 

 prepared soil, fine but not too rich, in small pots or boxes, and 

 to keep them in a cool part of the green-house, or in a frame. 



One plant, three feet across, so treated, produced last season, 

 in the nursery, over 1,000 of these young plants. 

 Somerville, Mass. — F. L. Temple. 



Principles of Physiological Botany, as Applied to 

 Horticulture and Forestry. 



VI.— Appropriation of Carbon, or Assimilation, 

 TipROM the previous papers in this series the following facts 

 ■*- must be briefly cited: (i) The parts of the plants are per- 

 fectly continuous, and there exists an unbroken connection 

 between the leaves on the minor divisions of the branches 

 and the hairs on the ultimate divisions of the roots. (2) That 

 all the active parts of the plant are impregnated with water, 

 and so long as the loss by evaporation from the leaves is 

 made good by receipt of water from the soil, the tissues 

 remain unwilted. (3) By evaporation of water from the leaves, 

 the dilute solutions taken in by osmose through the root-hairs 

 are concentrated. (4) That the active cells throughout the 

 plant require, for their activity, oxygen and food. 



We are now to inquire in what way the plant prepares for 

 itself this food which is essential to its acdvity.. The question 

 will be simpler if we look first at the mechanism of the food 

 factory itself, the green leaves and other green tissues 

 exposed to light, afterwards considering the materials out of 

 which the food is made. 



Each green leaf consists of a framework made up of 

 mechanical elements imparting strength to the fabric. This 

 framework gives us the innumerable diversities of veining 

 of leaves, and their distribution governs largely the shape of 

 the leaves. Supported by the framework are the active cells 

 by which the food is prepared. In most cases these are not 

 closely packed together, but they have between them inter- 

 cellular spaces of greater or smaller size. Over the whole is 

 extended the delicate epidermis, with its breathing-pores, 

 previously described. The active cells contain not only pro- 

 toplasm, but also green plastids or chlorophyll-granules. The 

 pigment which gives to these their characteristic color pos- 

 sesses peculiar optical properties, chief among which is that 

 of modifying the refrangibility of the rays of light, so tliat all 

 the so-called violet, indigo, blue, green and yellow rays are 

 bent from their course, and appear as red rays. Again, the 

 color of an alcoholic solution of this pigment, which by 

 transmitted light is green, appears blood-red by reflected light. 



By gaseous diffusion the gases of atmospheric air make 

 their way through the epidermis, and come, in a dissolved 

 state, into contact with the protoplasmic matter and the green 



granules vvhicli it contains. In the atmosphere there is found, 

 in very small amount, the gas known as carbon-dioxide. This 

 gas and the water from the soil are the principal raw materials 

 used in the manufacture of food. Formerly the amount of 

 carbon-dioxide in the atmosphere was stated to be about four 

 hundredths of one per cent, but recent investigations have 

 placed the figure somewhat lower, or about three one- 

 hundredths of one per cent. This incredibly small amount 

 is the source of all the carbon which we find in the organic 

 world. It IS first appropriated by the green granules under 

 certain conditions about to be noticed, and, once appropriated, 

 its combinations undergo myriads of transformations, both in 

 the vegetable and animal kingdoms. 



The conditions for the appropriation of carbo7i by plants may 

 be given in the following order: (i) A supply of carbon- 

 dioxide adequate in amount, but still not largely in excess of 

 what the plant naturally finds around it in our atmosphere. 

 It is generally believed that at certain periods in the geologi- 

 cal past the amount might have been somewhat larger than 

 that which we find at present. It is not, however, necessary 

 to hold that the percentage was very much greater, in order to 

 account for the enormous accumulations of vegetable matter 

 transformed into coal during the carboniferous period. Bota- 

 nists think that plants obtain the carbon-dioxide directly from 

 the atmosphere, and all the experiments upon the subject 

 justify that conclusion; but it seems unlikely that plants are 

 unable, under any circumstances, to obtain a certain portion 

 from the soil. The late Professor Gray believed that plants 

 possess the power of taking up some of their carbon-dioxide 

 through their roots, but he frankly said, that as yet we have no 

 actual proof that this is the case. 



(2) The second condition for the appropriation of carbon is 

 the presence of chlorophyll granules in active protoplasm. 

 Protoplasm without these granules (or their equivalent, like 

 that found in certain sea-weeds), does not have the power of 

 effecting the change by which carbon is retained. Again (3), 

 there must be exposure of the cells to light of proper quality 

 and intensity, such as that furnished in the sun's rays. It is 

 not necessary, for experimental purposes, that the light should 

 be direct or diffused sunlight, for some of the common arti- 

 ficial lights answer, notably the brilliant electrical lights now 

 in use. But, of course, in its ultimate analysis, all of these 

 artificial lights are only sunlight more or less removed from its 

 original source. 



Lastly (4), the active cells must be kept at a certain tempera- 

 ture. The degree of temperature most favorable for most 

 rapid appropriation of carbon is different for different plants, 

 but, in general, it is not far from 85" to 90° Fahr. 



When these conditions are provided, the manufacture of 

 food proceeds with greater or less rapidity, the rate depending 

 on certain minor factors. Its chief feature is the reduction of 

 the carbon-dioxide in the presence of water by the elimination 

 of a certain proportion of the oxygen of these two substances, 

 amounting practically to that which the carbon-dioxide holds in 

 combination. This oxygen is set free from its combination, 

 and, for the most part, escapes from the plant. 



We do not know positively what the resultant combination 

 of carbon, hydrogen and oxygen is, but it is probably one of 

 the simplest carbohydrates, capable of immediate transforma- 

 tion into other substances. It is easy to show that, under cer- 

 tain circumstances, a part of this food is changed into starch, 

 even in the chlorophyll granule, and there held in its solid 

 form. But the greater part is taken away from the source of 

 manufacture and stored in some shape for immediate or for 

 future use. A large portion of this food is changed at once 

 into the permanent form of cellulose or cell-wall substance. 

 Portions are changed in the laboratory of the plant into the 

 numerous substances characteristic of the vegetable world, 

 such as tannin-like matters, and so on. And since all these 

 substances formed from inorganic matter are like plant-sub- 

 stance, the term assimilation has been applied to the process 

 by which they are formed. But, lastly, a certain part is con- 

 sumed at once in work ; combining with oxygen, it is, so to 

 speak, burned up in doing the proper work of the plant. This 

 proper work of the plant — its lifting and growth, its transfers 

 of material and the motions of its parts — must be regarded as 

 very small when compared with that which is done by sun- 

 light in the plant. This can be illustrated by giving an ap- 

 proximate estimate of the amount of carbon -which plants 

 accumulate during a given time. This accumulation ex- 

 presses, of course, the amount of work done by the sunlight 

 in breaking up carbon-dioxide, less the amount of food broken 

 up by the plant in its own activities. The difference is well 

 seen when we take an acre of forest and estimate its annual 

 increase in carbon. This is about the same as that accu- 



