For September. 1921 



707 



A Lesson on Vegetative Plant Reproduction 



Being One of a Series of Lessons of a Home Study Course on Gardening Appearing Regularly in The Gardeners' Chronicle 



Under the Direction of ARTHUR SMITH 



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TAKEN in a wide and general sense, the most distinctive 

 difference between a plant and an animal is that the latter 

 cannot be reproduced from any of its parts, nor otherwise 

 than from a fertilized egg. While it is true that we can take a 

 certain part from one animal and graft it on to another of the 

 same species, or even a different species, we cannot take away 

 any portion and grow it into a perfect organism. 



With a plant, however, we can take a shoot or other detachable 

 part, such as shoots, bulbs, bulb-scales, tubers, buds, and leaves, 

 and from these produce perfect plants ; all these forms of plant 

 reproduction and others of a similar nature, being known as vege- 

 tative, in contradistinction to reproduction from seed. 



By the use of the vegetative — technically, asexual — method of 

 plant multiplication we are practically certain to obtain plants 

 alike in every respect to those from which the parts have been 

 taken, whicli is not always the case with reproduction from 

 seed; in fact the ase.\ual process is, in the majority of cases, the 

 only means of reproducing varieties — as destinct from species — 

 with certainty. 



.\s we have before pointed out, growth, in both plants and 

 animals, takes place only by the multiplication of individual cells. 

 From facts as they stand it appear certain that the plant-cell 

 contains within itself all the elements required to produce a perfect 

 plant, which is evidently not the case with the animal-cell. 



The most common method of multiplying plants by the vege- 

 tative meUiod is by cutting off a shoot, root, or leaf of a plant, 

 and placing the portion removed under such conditions that some 

 at least of the living cells will produce roots, and by this means 

 an entirely new plant can be brought into existence. 



In all living organisms, whether plants or animals, we find 

 that cells have the inherent power of forming what mav be 

 termed, healing or protective tissues. The use of gardening tools 

 may cause abrasions of the skin cr blisters to form on one's 

 hands ; it will not be long, however, before a thickened protective 

 skin will be grown over these places. When a branch is cut from 

 a tree the living cells of the inner bark, or cambium, will soon — 

 sooner in the growing season than when the tree is dormant — 

 commence a growth which will ultimately cover the wound, this 

 growth is known as a callus. The reason for painting the part 

 from which a branch has been removed is to prevent the entrance 

 of fungi causing decay until the new tissue covers the wound, 

 which will eventually be the case if complete healing results. 



.\s a rule, the first apparent change in a cutting of woodv 

 plants is the formation of a callus upon the lower end. and it is 

 commonly thought that this process must be well progressed be- 

 fore roots can form. But roots do not arise from the callus itself 

 but from the internal tissue, and in many cases they appear to 

 bear no relation to the callus in position. In willows for instance, 

 roots arise through the bark at some distance above the callus. 

 Further, a callus may form on a cutting which never roots at all. 

 At the same time the best results are obtained from callused cut- 

 tings, especially if the cuttings arc from mature wood. This, 

 however, is probably due to the fact that some time generally has 

 to elapse before the fomiation of the adventititous buds which 

 give rise to riM)ts are formed, and not to any connection between 

 the callusing and the rooting process. Undoubtedly the forma- 

 tion of a callus at the bottom of a cutting is Nature's method of 

 preventing decay, or at least of holding it off until roots are 

 formed; roots rarely, if ever, grow from a cutting after the decay 

 of the bottom has conmienced. 



It is a singular fact that the lower, or proximal, end of the cut- 

 ting as it stood upon the parent plant, produces roots, and the 

 upix-r, or distal, end. produces leaves and shoots ; if the cutting 

 is inverted so that the top is placed in the soil roots will never 

 arise from it. This is true in principle even of root-cnttings ; it 

 is only at the end which grew nearest to the plant that roots arc 

 produced. If a cuttin,? is divided into several parts, each part 

 will exhibit the same differentiation of function. The reasons for 

 this wonderful localization of function are not undcsfocxl. al- 

 though the phenomenon has frequently been the subject of studv. 

 but it appears undoul>tcdly to be one of the numerous examples 

 of the Directivity of Life which abound in Nature. 



Nearly all plants mav be propa.gated by cutting from one < r 

 another of their parts, but the ease with which they can be mu'- 

 tiplicd in this way varies considerably with different species, and 

 with even varieties of the same species. 



Climate no doubt exerts a marked influence upon the tendency 

 of plants to develop from cuttings. In certain localities in south- 

 ern Europe and parts of South America, branches of the apple 

 tree sharpened and driven into the ground often take root and 

 sometimes even bear fruit during the same season. ."Xgain. with 

 some species like the willow, a stem will root under almost any 

 conditions. In practically all cases a warm, moist atmosphere is 

 the most favorable condition for the propagation of cuttings. 



The part of plants to be used for stem cuttings are preferably 

 the younger, matured growth, since the tissues of these are the 

 most vigorous. The cutting should always contain one or more 

 buds. A soil warmer than the air above it is important in many 

 cases, as warmth stimulates growth, and when applied to one part 

 of a plant it stimulates the growth of that part. If the soil about 

 a planted cutting is warmed to a temperature considerably higher 

 than that of the air above it, the growth of the roots is stimu- 

 lated; in fact bottom heat often excites growth in cuttings which 

 will not root without it. On the other hand when the soil is 

 much cooler than the air, if the temperature of the latter is high 

 enough, leaf growth is stimulated before that of roots, and 

 before the latter are former the vigor of the cutting is reduced 

 or perhaps entirely exhausted. 



Since we have better facilities for raising than for low-ering 

 the natural temperature, propagation from cuttings is easier at 

 a time of year when the temperature of the atmosphere does not 

 much exceed fifty degrees. By observing special precautions, how- 

 ever, it is possible to propagate many plants from cuttings during 

 the warm season. 



With cuttings having leaves upon them, transpiration must 

 be reduced to a minimum until roots are formed, because water 

 cannot be freely taken up without the existence of root-hairs. 

 For such cuttings, therefore, the air as well as the soil must be 

 kept abundantly moist, and during the greater part of the dav the 

 direct rays of the sun must be intercepted by shading. 



The alternations of temperature in the open air are as a rule 

 unfavorable to the development of cuttings, although many plants 

 are readily propagated by cuttings out of doors. Invariably, 

 therefore, some structure which will confine warmth radiated 

 from the ground, or artificially generated, as by a hot-bed. or that 

 may when necessary shut out part of the solar heat, is alwavs 

 of great assistance in rooting cuttings, and in many species is 

 essential to success. 



Outside a greenhouse specially arranged for propagatin.g a 

 cold frame is the simplest structure for a number of cuttin.gs. 

 For a small quantity a box which can be covered with a sheet ot 

 glass answers every purpose, and a bell-jar or even a fruit bottle 

 can be inverted over cuttings. With these simple appliances many 

 plants may be successfully propagated by cuttings during .Au- 

 gust and September, among which may be mentioned roses, cur- 

 rants, gooseberries, most shrubs and other hard-wo<xied sub- 

 jects. In these cases cuttings should be of the current vear's 

 growth, which have become firm ; soft, very young .growth is in 

 these cases of no value for the purpose. In the case of soft- 

 wooded plants like fibrous- rooted begonias, coleuses, geraniums, 

 it is the younger growtli which is used. 



Sand is invariably the best material in which to insert cuttings, 

 and the cutting-box or bed must be well-drained. Some plants 

 will root freely in ordinary garden soil, or in pure water. Sand 

 should be clean, rather coarse and sharp, but it needs to be 

 selected with care as it often contains injurious mineral matters. 

 Sand found along the borders of fresh-water streams may gen- 

 erally be used without washing, 'out that dug from sand pits 

 should invariably be exposed to the sun for a few weeks and 

 then thoroughly washed before being employed for cuttings. It 

 should always be free from organic matter and decaying material 

 in sand favors disease. The same sand should be used for but 

 one lot of cuttings, for it is liable to become infested with fungi. 



With soft-woode<i plants, damping off of the cuttings frequent- 

 ly causes trouble. This may to a great extent be prevented by 

 sterilizing the sand, and for this purpose small quantities mav be 

 baketl in an oven or scalded with boiling water. The .glass cover- 

 ing should be removed daily and the condensed moisture wiped 

 off it. 



For convenience we seperate stem cuttin.gs into two divisions, 

 namely, those from dormant, and those from active, plants, as 

 the requirements of these two classes differ in some respects. 



