32 



Garden and Forest. 



[January i6, li 



Orchid Notes. 



Cattleya Triana. — This magnificent winter flowering Cat- 

 tleya has now commenced to enrich our Orchid houses with 

 its large and very handsome blossoms. A great treat is in 

 store for those who may visit the collections of Messrs. Kim- 

 ball, Corning, Ames and others, where these plants are to be 

 seen rapidly developing their enormous flowers, which are 

 remarkable for great variation and brilliancy of color. At a 

 recent visit to Mr. De Forest's Orchid houses at Summit, New 

 Jersey, this Cattleya was seen by the thousand, abundantly 

 furnished with foliage and literally covered with flower 

 sheaths. Some flowers were already expanded, having label- 

 lums of a fine magenta purple, and exquisitely fringed. Besides 

 this variety, there were hundreds of C. Mossice, C. Bowri?igeana, 

 C. Percivaliana, C. Gaskelliana and many other free flowering 

 varieties. It is safe to assert that thepossessor of this vast num- 

 ber of plants is the largest Cattleya-grower in the country. As 

 a florist's flower, C. Triana is fast becoming popular, as it 

 blooms at a season when flowers are in great demand, and its 

 easy culture, with the abundance and lasting quality of its 

 flowers, make it a specially desirable Orchid. During the 

 months of March and April importations of this species gen- 

 erally arrive. They are then in a dormant condition, and this 

 will also be found a very convenient season to commence es- 

 tablishing them, as the spring and summer months enable 

 the plants to make strong and satisfactory growth. They en- 

 joy a mixture of rough fibrous peat, clean sphagnum in small 

 quantities, with charcoal added, which last is a sure preventive 

 of stagnant compost. When making their growth full sun- 

 light should be kept from them carefully, as the foliage is not 

 so robust as that of C. El-Dorado, C. speciosissima, C. Walker- 

 iana, and such varieties. All thin-leaved Cattleyas, such as C. 

 iMendelii, C. Chocoensis, C. Gaskelliana, C. Percivaliana, would 

 grow as well if not fully exposed to direct sunlight, as good, 

 sturdy growths and bold, substantial blossoms are easily ob- 

 tained by giving the plants a thorough rest after flowering, 

 and an abundant supply of pure air and moisture during their 

 growing period. A. D. 



Principles of Physiological Botany as Applied to 



Horticulture and Forestry. 



III.— The Absorption of Liquids by Plants — The Transfer of 

 Water from the Soil to the Roots. 



THAT plants have in their composition a large proportion 

 of water is a very familiar fact. The amount of water 

 differs in different kinds of plants, in different parts of the same 

 plant, and, as has been repeatedly shown by experiment, in 

 the same part at different seasons. Illustrations of these dif- 

 ferences will occur to every one upon reflection, and do not 

 require to be further examined at this time. But, back of these 

 differences lies a fact that a certain percentage of water in 

 plants is essential to their activity. When this amount is 

 diminished below a certain point the activity of the plant is 

 diminished, and, if the lack is long-continued, the life of the 

 plant is imperiled. The first case is well illustrated by the 

 slow ripening of seeds, the latter is too often illustrated in 

 times of drought. 



Part of the water in the plant exists as liquid water in the 

 sap of the active cells. In what are popularly called the pores 

 of wood — namely, the microscopic tubular bodies known as 

 ducts — producedby a peculiar development of coherent ceUs — 

 it is rather uncommon to find any liquid water, although this 

 does occur at times. The sides of the ducts are moist, and 

 the whole wall seems to be saturated -with water, but the cavi- 

 ties themselves do not generally contain any water at all. In 

 these and similar cases it is believed that the water exists in a 

 combined state so thoroughly incorporated with the substance 

 of the walls of the long cells and ducts that it cannot be dis- 

 cerned as water. But it can be proved to exist there by the 

 simple experiment of drying the whole. It is not, however, 

 very clear in what way the water is combined with the cell- 

 wall substance in plants. One theory, which has met with 

 general recognition as capable of explaining a large number 

 of facts, is that the water surrounds each structural molecule 

 as a delicate film which is practically continuous with the 

 films nearest to it, and thus all the water throughout the 

 plant is a connected whole which, under normal conditions, is 

 in a state of equilibrium very easily disturbed. Thus it can 

 be disturbed by the evaporation of the films of water around 

 the structural molecules in foliage, which makes a demand 

 upon the supply of water below the point of loss, and so on 

 down the whole stem, until the roots are reached, and here, 

 of course, all further supply must come from the soil. This 



transfer can be easily examined in the case of our forest trees 

 and shrubs after we have ascertained the manner in which the 

 loss from evaporation can be made good by means of the 

 roots. Under ordinary circumstances no water even in the 

 state of vapor is absorbed by leaves. 



Microscopic Structure of Roots.— The structure of 

 roots can be most readily understood by confining our atten- 

 tion at first to the parts of the root which are near the end 

 of the delicate root-branches. These parts may be considered 

 in the order of their succession, beginning at the very tip. 

 The extreme tip has, in the case of our common plants now 

 under consideration, a well-marked cap of a protective nature, 

 made up of somewhat flattened cells constituting a hollow 

 cone, in the inner angle of which is a group of cells. Each of 

 these cells is completely filled with protoplasm, and is 

 actively engaged in the work of producing new cells ; hence 

 the group is conveniently known as the "growing point." 

 New cells are formed in front and around this growing 

 point, and these new cells, through changes in their size 

 and shape, serve to extend the rootlet by terminal growth. 

 Thus the minute rootlets are ever reaching forth into new soil, 

 into the crevices of which they can, owing to their minute 

 size, make their way. After they have crept into the inter- 

 stices of the soil, they thicken up sooner or later, while far 

 ahead of the thickening parts is the still advancing point of 

 growth protected by its root-cap. 



The tip of the root is not, however, a passive thing, merely 

 pushed forward by something behind it ; it possesses sensi- 

 tiveness and the power of spontaneous motion. It is con- 

 stantly revolving within a very narrow orbit. When it is in the 

 soil, this motion is wholly obscured by the crowding of the 

 particles of earth, nevertheless by this restricted motion in a 

 cramped space, the tip can work along almost as if in search 

 of a pathway. Moreover, the tip by its dull sensitiveness can 

 distinguish between particles of soil which have different 

 physical properties, and thus, one might say, choose its 

 course. The description of the marvelous faculties possessed 

 by the tip of the rootlet, as given in the " Power of Move- 

 ment in Plants," is among the most interesting of the writings 

 of the late Charles Darwin. 



Root-Hairs and Other Absorbing Cells.* — It was formerly 

 thought that the tip of the root, having, as appears under the 

 microscope, a sort of spongy structure, is the efficient agent 

 in soaking up moisture from the soil. But it is now well 

 known that it is the cells which lie just behind the tip of the 

 young rootlets which perform the work of absorption. These 

 thin-walled cells on the surface of the rootlet, just behind its 

 tip, are in most cases associated with peculiar cells which 

 have slender outgrowths or prolongations like hairs, and 

 these are sometimes so thickly crowded together that they 

 give to the narrow zone the appearance of white or almost 

 colorless velvet. The root-hairs are transient, working actively 

 for a time, and then falling off, but the newer parts of the ex- 

 tending rootlets are continuously provided with fresh ones, 

 and thus the supply of absorbing organs is constantly increas- 

 ing just in proportion to the branching of roots and the forma- 

 tion of new rootlets, each of which is, of course, furnished 

 with its zone of plant-hairs. And, furthermore, from the man- 

 ner of growth, the new root-hairs are formed just where they 

 can find fresh soil for their work of absorption, ever foraging 

 through new fields. 



The root-hairs come into most intimate contact with parti- 

 cles of soil, and undergo, in many if not most cases, a modifi- 

 cation of their walls which may be said to glue them to the 

 contiguous particles. It is probable, but not yet positively 

 proved, that they exert a slight solvent action even upon some 

 sorts of soil which appear to be otherwise practically insoluble 

 in any aqueous solutions. As we shall later see, when we ex- 

 amine the action of the tip during the process of growth, there 

 is always a slight excretion of an acid at the tip itself. Soil- 

 water, as well as the water of our rivers and ponds, contains 

 in solution small amounts of various mineral and other mat- 

 ters, and these in certain proportions are absorbed by the 

 rootlets through the mechanism before described. The min- 

 eral substances are. for the most part, compounds of the fol- 

 lowing elements (chiefly with phosphoric and sulphuric acids, 

 together with chlorine): Calcium, magnesium, potassium, 

 iron, and others in smaller amount. Besides these, certain 

 compounds of nitrogen are absorbed. The origin and desti- 

 nation of all these substances will be discussed when we take 

 up the subject of nutrition. 



Osmose. — Absorption of liquids takes place through the 

 activity of the superficial portion of the thin layer of proto- 



* Another possible manner in which roots may absorb \vill be taken up for con- 

 sideration in a subsequent paper of this series. 



