474 



GARDFMERS' CHRONICLE 



not generally noticed. There are, nevertheless, minute and effec- 

 tive structures invariably present in great abundance, known as 

 root-hairs, which arise from the surface of all young and grow- 

 ing roots. As soon as the root in germination has attained tn 

 the length of about an inch these root-hairs are developed at a 

 short distance behind the root-tip. They arise practically per- 

 pendicular to the surface, and an examination under a microscope 

 indicates that they are simple, elongated cells, consisting of a 

 rather resistant cell-wall within which is contained granular 

 protoplasm and cell-sap. Root-hairs may become very evident if 

 we artiticially germinate seeds, of radish for instance, between 

 sheets of moist filter-paper or flannel, and when grown in this 

 way the hairs assume generally a greater length than in the soil, 

 and they arc, as well, perfectly straight tubes. As they develop 

 in the soil, however, where the numerous particles of earth 

 obstruct their growth they bend about and flatten out against 

 and around these particles, becoming as a result contorted and 

 deformed in appearance. It is evident that they come into the 

 most intimate contact with the minute grains of soil, so much 

 so that these latter actually stick into the walls of the hairs ; bv 

 this means the hairs are peculiarly adapted for the purpose of 

 absorption. 



Root-hairs develop just behind the elongating part of the 

 rootlet, and their use is to absorb water with the food materials 

 it contains in solution. As the e.xtremity of the root advances 

 through the soil by growth, new root-hairs are formed in front 

 of the older ones, while those farthest back as rapidly die oft'. 

 so that only a short portion of a root bears hairs at any one time. 

 It is usually difficult to see root-hairs growing in the soil, but 

 they may sometimes be discovered with the "aid of a pocket 

 magnifying glass by carefully removing the soil from about the 

 younger roots, when the silky network of root-hairs may be 

 seen filling the pores of the soil and enveloping the soil particles. 

 Only that part of the roots which is in front of the hairs is at 

 all active in absorption, in fact absorption is carried on almost 

 entirely through the hairs, and that portion of the root upon 

 which they have died is practically of no more value, so far as 

 absorption is concerned, its uses being confined to being a vehicle 

 for the conveyance of fluids, and for strengthening the plant's 

 position in the ground. The elongation of roots ceases upon that 

 portion on which root-hairs are formed, this elongation being 

 strictly confined to the portion between the hairs and the tip; 

 subsequently roots only grow in diameter in much the same 

 manner as the stem increases in si/e. 



It is therefore obvious that wc should aim at creating such 

 soil environment as will conduce to the existence of the greatest 

 number of root-tips ; this is brought by the encouragement of 

 root-branching. Roots never branch freely in a hard, lumpy 

 soil. The greater the number of branches the greater the nnmlier 

 of root-hairs, and the fact must be again emphasized that these 

 hairs are the most important part of roots as it is through them 

 that almost all of a plant's food and drink is absorbed, and the 

 hairs only grow just behind the young, growing roots. When 

 first formed root-branches are as fine as ordinary hairs, but 

 these branches must not be confounded with root-hairs, and the 

 latter never develop into branches. 



Root growth is always excited by suitable soil conditions, but 

 a continual sufficiency of moisture appears to have the greatest 

 exciting cause. Roots frequently develop from parts of a stem 

 that remains for a certain time in contact with moisture. In the 

 tropics, where the air is very moist, some plants, in addition to 

 the previously mentioned orchids, emit roots very freely from 

 the stem aliove ground, and a marked example of this is seen in 

 the case of Ficiis indica (Banyan Tree). Cuttings form roots 

 Iiecause they are kept in contact with abundant water at a suitable 

 temperature, and cuttings of some plants will root in water alone. 

 As the cells of new roots are full of protoplasm, they must 

 have access to the oxygen of the air or they will neither live 

 nor grow. This is clearly shown by the following experiment : 

 After thoroughly boiling some water to expel its oxygen pour 

 some of it into two glass tumblers, filling them up to within 

 half an inch of the top; into one pour enough oil — olive or other 

 of a vegetable origin — to cover the water with a film not less 

 than an eighth of an inch thick to prevent any oxygen from re- 

 entering the water. When cool enough place a rooted cutting 

 into each glass ; the roots of the one in the water exposed to the 

 air will continue to live, but in the other case where the supply 

 of oxygen is cut off by the oil film, the roots will die. The total 

 absence of live rootlets in the puddled clods of badly tilled soil 

 shows that they will not penetrate soil from which air has been 

 expelled, or into which air cannot enter from want of cultivation. 

 The roots of practically all garden plants will refuse to enter 

 a water-logged soil and if they were already in the soil before 

 it became water-logged, such a condition w'ill result in their death 

 practically b\- suft'ocation. 



Planting trees too deeply or raising the soil under trees when 

 grading may result in death owing to the roots not getting 



sufticient air. W hen it is necessary to raise ground abuut trees 

 access ot air to their roots can be provided for by making a well 

 around and at some distance away from their trunks 



Bearing in mind the fact above indicated that, so far as growth 

 IS concerned, the most valuable portion of roots is that from 

 where the root-hairs begin up to the tip, it is very plain that the 

 greatest success in transplanting is only achieved by the most 

 careful handling of the plant's roots. Carelessness in lifting a 

 plant from the position m which it has been growing is a fruitful 

 source ot failure m transplanting, especially with nursery stock 

 which carelessness results in the destruction of the fine "rootlets' 

 and their accompanying root-hairs. When the lifting has been 

 properly done the same result may be brought about by allowing 

 he fine rootlets to be killed hy exposure to drving influences 

 between the time the plant was taken out from the soil and the 

 time It was planted into its new position. Under these circum- 

 stances before root action can again come into work new root- 

 ets and root-ha.rs must be grown. Whether the plant survives 

 the shock of transplanting, or not, will depend upon the length 

 ot time which elapses before new root-action takes place Re- 

 ne\ved root-action is frequently retarded, or even prevented en- 

 tirely, by covering the roots with too rich a soil which has 



ecome sour Renewal of root growth is greatly hastened b 

 covering with sharp sand ; cuttings of plants always root more 

 treely in sand than m anything else, and for all practical pur- 

 poses the growing of new roots from old ones involves the same 

 processes and conditions as the growing of roots from a cutting 

 in the case of things which are never sown in their permanent 

 position, annual flower and vegetable plants for example the 

 practice of growing them in paper pots, or in what are called 



airt bands is greatly to be recommended. With this method 



or band, and however careless or ignorant the planter, it woiild 

 n this way require considerable effort to inflict damage upon 

 ireatK f'; 'U^' P^^^^^^^^'on of root-hairs in transplauHng'^ is 

 greatly facilitated by removing as much soil as possible with the 

 plant. To this end the practice of balling and burlaping is used 

 m connection with the removal of certain plants from the nursery 

 \Vhen taking up seedlings from a seed-bed the root-hairs should 

 not be destroyed by pulling up the plants, but should be pre- 

 served by lifting with a trowel. When the soil is dry at trans- 

 planting time reduction of the shock is greatlv brought about bv 

 thoroughly soaking the ground around them the dav before ih 

 all cases where death ensues from transplanting it 'is caused bv 

 the roots not having received proper care during or after the 

 operation. 



\yiiile the minute size of the root-hairs will naturally prevent 

 a single hair from performing much in the wav of absorption 

 still, when we realize that there are millions of these hairs con- 

 nected with one root system, all co-operating to the same end 

 It IS easy to understand that the aggregate of absorption results 

 m considerable force being accumulated. It is this which causes 

 sap to flow so freely from pruned or injured stems during the 

 growing season. From experiment it has been proved that this 

 absorptive power is most active when the soil is warm, and that 

 withm certain limits it decreases with falling temperature and 

 increases with a rising one ; and this is irrespective of the atmos- 

 pheric conditions above ground. When the soil is warm the 

 absorptive power of root-hairs may be sufficient to force water 

 from the tips of leaves during cool nights when transpiration is 

 slight. 



In addition to their work of absorption, roots have to excrete 

 much of the carbonic acid formed in the plant during its life 

 processes. This acid acts upon unavailable mineral plant food 

 and renders it available, and in this way roots may be said to 

 make part of their own food. This is clearly proved when plants 

 are grown upon a limestone slab on which the roots will etch 

 out grooves. The same thing occurs when plants like lichens 

 and mosses will eat away the surface of hard rocks and so start 

 the formation of soil. The excretions of substances from the 

 roots of one plant wdiich may be poisonous to others has long 

 been under consideration, and over half a century ago De 

 Candolle held this view. This idea has at the present time, 

 however, little support. 



Tlie results of recent studies along these lines seem to point 

 to an oxidizing action in the soil by roots, and while such a 

 process, if it exists, may be of practical importance, there ap- 

 pears little doubt that such action must be very small compared 

 with the effect of the excreted carbonic acid in dissolving plant 

 food out of insoluble mineral matter. 



It may be noted that carbonic acid is an excrete product of the 

 protoplasm of every active plant cell. 



New York Spring Flower Show — March 14-20 

 Boston Spring Flower Show — April 6-10 



