140 



Garden and Forest. 



[March 20, if 



narrower, smaller leaflets, much more rounded at the tips 

 than those of its American relative. Judging from the aspect 

 of the yoimg plants the species seems likely to prove a quicker 

 grower than the Kentucky Coffee-tree. In the Kew Herbarium 

 thereisagoodseriesof driedspecimens of G. Chinensis. These 

 exhibit a niarked character in the pod, which is only half the 

 size of that of G. dioicus, and the foliage, as is already stated, 

 is very different from that of the American plant. 



On one of the tickets attached to part of Dr. Henry's mate- 

 rial is the following information : "The soft substance inside 

 the pod is used for washing the face by Chinese women. The 

 seeds themselves are strung together and made into a sort of 

 ' chain-armor' undershirt for wearing next the skin in summer 

 by coolies." To a sample of pods in the Museum No. i is af- 

 fixed the following : "They are beaten with a mallet and used 

 as soap. Sold at about sixteen to twenty a penny." 



It seems desirable to put on record the exact date of the in- 

 troduction to cultivation in Europe of a most interesting and, 

 what may also prove, a valuable tree. I have, with this ob- 

 ject, penned the foregoing lines. So far as I know they form 

 the first record of the tree from the standpoint of the cultivator. 



Royal Gardens, Kew, February, 1889. George Nicholson. 



BoRONiA HETEROPHYLLA, figured and described in a recent 

 issue of the Revue Horticole, is a newly cultivated species of a 

 genus long known in gardens. It is a tall, glabrous shrub, 

 with numerous slender branches ; narrow, linear and some- 

 times pinnate leaves, and handsome and very fragrant 

 red flowers, which are produced in the greatest profusion 

 along the whole length of the stems. The Boronias are 

 all natives of Australia, and excellent cool green-house 

 plants. The present subject will probal>ly prove a more 

 vigorous grower than B. megastigma, the most commonly 

 cultivated species, the flowers of which are not surpassed 

 in delicacy and intensity of perfume, and it is pretty sure 

 to become a popular addition to our winter-blooming green- 

 house plants. B. heterophylla is said to have been intro- 

 duced into European gardens by Miss Marion North, the 

 celebrated traveler and flower-painter, whose collection of 

 paintings, made from nature in nearly every part of the world, 

 and presented by her to the English nation,, is one of the most 

 interesting features of Kew Gardens. 



Principles of Physiological Botany, as Applied to 



Horticulture and Forestry. 



XII. — The Growth of Organs. 



"D Y the multiplication of cells in the manner described in the 

 -'-' last paper, all the different organs of the plant are built 

 up and the several parts are joined together. The laying down 

 of the partition walls in these microscopic cells is never a hap- 

 hazard matter. Every plane and curve falls into its place in 

 obedience to the law of inheritance, and thus the sum of 

 shapes of the cells gives us the inheritance as a whole. 

 Hence, for example, the cell-growth of the Maple gives us the 

 Maple tree, differing in some essential particulars from every 

 other Maple tree, even of the same variety, having slight dif- 

 ferences, perhaps, in the distribudon of roots and buds and 

 branches, but still resembling its kin in all essential features, 

 so closely, indeed, that its relationships are easily recognized. 

 The laws of growth which underlie this remarkable uniformity 

 of shape in plants which are descended from a common stock 

 are not at all understood, though many of the facts bearing on 

 the subject have been recorded. Some of these may be noted 

 in connection with this portion of our subject; other facts re- 

 lafing to growth must be deferred to a later stage of our 

 examination. 



The order of study which will be found most convenient is, 

 first, the mode of growth of the organs in their order of suc- 

 cession ; second, the conditions of growth, and lastly, some of 

 the physical phenomena which accompany growth. 



Growth of the Root.— In the seeds of our common forest 

 trees the root exists as a single conical cluster of cells at the 

 end of a rudimentary stem. In the grasses and allied plants 

 the origin is multiple and somewhat different, but this need not 

 concern the present treatment of the subject. 



Growth of Roots in Length.— When the germ breaks 

 through the seed-coats the root is generally the first thing to 

 be seen, appearing at that period as a firm cone, which is seen 

 to consist of two essentially unlike parts, an outer cap of flat- 

 tened cells and a small group of minute cells in the hollow 

 point of this cap. The root extends in length by the multipli- 

 cation of the cells in this group. The renewal of the cap 

 keeps pace with the extension of the growing point, and thus 



the slender, thread-like form, protected at its extremity, insin- 

 uates itself through the crevices of the soil in which it could 

 not be forcibly thrust. Practically only a very short portion of 

 the root is at all capable of growth in length; in fact, it is gen- 

 erally said that only the protected tip can thus grow. As a 

 matter of fact, however, some of the extension is due to the 

 enlargement of the cells just behind the point of true cell-mul- 

 tiplication. 



Growth of Roots in Thickness. — The roots of our com- 

 mon forest trees and shrubs thicken by the addition of new 

 cells substantially in the same manner as that which is charac- 

 teristic of stems, to be described presently. _ 



Growth of Roots by Branching. — The arrangement of 

 roots is so much disguised by the distortions arising from the 

 pressure of the soil that there seems to be no sort of regular- 

 ity in their branching. But if roots are grown in water, espe- 

 cially water containing a sufficient supply of nutrient material, 

 their arrangement is seen to be one of a good degree of 

 symmetry. Each new root-branch starts naturally from a 

 group of cells lying very near what one may call the shaft of 

 the root. If, as happens when roots are closely pruned, the 

 new root-branches are very numerous, there is no regularity 

 at all in their distribution. Every root-branch, whether it 

 arises from a pruned or an unpruned root, is provided at its 

 slender tip with a root-cap precisely like that which belongs to 

 the earliest roots, and the growth is after the same fashion. But 

 there are a few differences in the directions taken by the main 

 and the lateral roots, some passing downwards in a far more 

 oblique course than the others. 



Under favorable circumstances roots can start from any 

 part of a stem, but they are more abundant at the joints than 

 at any other places. All these roots striking out from the 

 stem and branches obey nearly the same laws of growth which 

 we have already noticed in those which appear underground. 

 Thus, in striking cuttings, the roots which appear at the cut 

 end of a shoot are in all substantial features like those which 

 form in the natural way, as lateral branches in normal roots. 



The Growth of Stems in Length. — The promise of the 

 main stem of an ordinary forest tree is contained in the rudi- 

 mentary bud in the seed. This is, like all buds, a shortened 

 stem, in miniature, with most of its parts only dimly fore- 

 shadowed. When a bud unfolds, the future joints of the Stem 

 or branch are barely oudined, but as the development pro- 

 ceeds, these joints become well defined and the distance be- 

 tween them increases. In definite growth the end of the 

 developing stem is terminated by a newly-formed bud, and at 

 the close of the annual period of growth this new bud stands 

 ready to unfold when occasion offers. Under ordinary condi- 

 tions in our climate, the buds do not expand until the begin- 

 ning of the spring period of growth, but if the leaves of a 

 tree are swept off in summer by insects, it sometimes happens 

 that there will be two growths from buds in a single year. 

 In the case of plants which have what is called indefinite 

 growth, there is no true terminal bud, but the stem or branch 

 continues growing until it is stopped by frost; the growth in 

 the following year begins in the uninjured parts. 



It is difficult to realize that all the upward and lateral growth 

 of our trees is from buds, and that when a given bud has 

 ceased growing for the season, it has stopped its growth in 

 length once for all, and all further extension of the stem and 

 branches must be from the development of the newly-formed 

 buds. 



In case of injury to a terminal bud, some of the lateral buds 

 appear as if stimulated to accelerated growth, and one or 

 more of the off-shoots assumes the place of leader, and con- 

 tinues the upward development 



The branching is, of course, dependent on the arrangement 

 and the development of the lateral buds. Each bud is nor- 

 mally in the upper angle formed by a leaf with the stem, but 

 there are certain exceptions to this. The normal buds govern 

 the shape of the plant. 



Seldom do all the buds of a plant develop. Those which 

 remain inactive are soon covered up by the growth of the tree 

 as it thickens, but under certain circumstances some of the 

 buried buds may start into activity, 



Growth of Stems in Thickness. — Confining our exami- 

 nation, as before, to our common forest trees and shrubs, it 

 is to be noted that the stem, even in a very young state, can 

 be easily distinguished into bark, wood and pith, together with 

 thin plates of cellular tissue which fill the spaces between the 

 wedges of wood. Just outside of the wood and under the 

 bark is found a layer of cells (or more than a single 

 layer), which possess the power of growth to form an inner 

 part of the bark and an outer layer of wood, while at the 

 same time it can keep itself in repair. This development of 



