BETTER FRUIT 



AN ILLUSTRATED MAGAZINE PUBLISHED MONTHLY IN THE INTEREST OF MODERN. PROGRESSIVE FRUIT GROWING AND MARKETING 



Pruning — Plant Physiology as Related to Pruning 



By W. M. Atwood, Associate Professor o 



[iNTHODUCTioN. — The Department of Botany, 

 in co-operation with the Division of Horticul- 

 ture, has prepared this treatise on pruning. 

 Dr. Atwood of the Department of Botany pre- 

 paring the chapter on Plant Physiology as Be- 

 lated to Pruning. The Division of Horticulture 

 has been working for a number of years on 

 research problems related to pruning. As this 

 work is in the preliminary stages, it will be a 

 number of years before a complete report can 

 be made. However, in the various papers in 

 this article we are presenting a few of the 

 facts which we have been able to determine, 

 coupled w ith observations that have been made 

 in various fruit-growing districts. — C. I. Lewis, 

 Chief, Division of Horticulture.] 



FOR the orchardist most correctly to 

 deal with the problems confronting 

 him, it is necessary to have a clear 

 idea of the complicated "living machin- 

 ery" upon which he is dependent for 

 profit or loss. It is worth while to 

 know how the tree removes from the 

 soil the substances it needs; how it 

 manufactures its food, and finally how 

 both the complicated 

 food materials and 

 water are distributed 

 and used by the tree. 

 The knowledge of a 

 few facts of this na- 

 ture is the necessary 

 foundation on which 

 is being built the suc- 

 cessful practices of 

 the practical fruit 

 grower of today. 



If the finest ter- 

 minal roots of most 

 living plants be care- 

 fully examined there 

 is found on their sur- 

 faces a fuzzy growth 

 resembling fine hairs. 

 As the root is the 

 region in which the 

 plant absorbs the 

 water and minerals 

 of the soil, it is evi- 

 dent that this absorb- 

 ing region of the root 

 — the root hair region 

 — must tremendously increase the ab- 

 sorbing area of the root. Figure 1 

 shows a young root with the root hair 

 zone well developed. These fine out- 

 growths of the root enable it to get into 

 very intimate contact with the finest 

 soil particles which contain necessary 

 minerals and which are surrounded by 

 films of soil-moisture that become avail- 

 able to the plant. The necessity of 

 carefully guarding the root hair region 

 of trees from injury so far as is possi- 

 ble is emphasized by the behavior of 

 any young tree upon transplanting. 

 Figure 2 shows the way in which a 

 twig of a pine tree was affected by 

 transplanting. It is evident that in 



Figure 1. Se<!dling 

 of radish showing 

 root hairs. (After 

 B.M.Duggar, "Plant 

 Physiology." Mac- 

 millans.) 



f Botany, Department of Horticulture Experiment Station, Oregon Agricultural College 



transplanting, the tree loses a large per- 

 centage of the finer roots, and hence of 

 the most active water-absorbing tissues. 

 The region where the needles were 

 so noticeably shortened is the region 



[Editor's Note. — This is the first of a series 

 of articles covering completely the subject of 

 "Pruning" that will appear in "Better Fruit." 

 "The Study of Fruit Buds," by E. J. Kraus, 

 will appear in the October edition. "Pruning 

 Young Trees," by Professor C. I. Lewis, will 

 appear in the November and December issues. 

 "Pruning the Bearing Apple and Pear Tree," 

 by V. R. Gardner, will appear in the January 

 issue. "Pruning the Bearing Prune Tree," by 

 V. R. Gardner, will appear in the February 

 issue.] 



thin outer wall there is a lining of the 

 jelly-like living substance called proto- 

 plasm, which is present in all animals 

 and plants wherever there is life. Water 

 tends to be taken into the root hair by 

 a force called osmosis. When pure 

 water is separated from the cell sub- 

 stances by the thin film of protoplasm, 

 we find that the water can readily enter 

 but the substances within the hair can- 

 not get outside of the protoplasm. The 

 law of osmosis is that when two liquids 



Figure 2. Effect of transplanting 

 upon water supply. Short needles 

 produced after transplanting. (After 

 B. M. Duggar, "Plant Physiology." 

 Macmillans.) 



which developed immediately following 

 transplanting and before the pine had 

 been able to develop new water-absorb- 

 ing root tissues. It thus becomes per- 

 fectly clear why the orchardist when 

 purchasing trees from a nursery never 

 leaves a large leafy top after first set- 

 ting out the young tree. Temporarily 

 the young tree is less able to supply its 

 leaves with water than previous to its 

 removal from the nursery. The judi- 

 cious cutting back of the top for a little 

 while enables the tree soon to develop 

 its root system back into balance with 

 the top. 



The root hairs do not absorb water 

 from the soil as a sponge or blotter 

 takes up water when placed in a wet 

 place. If a root hair is examined under 

 a microscope we find that inside the 



Figure 3. Root Cells. "A," in normal 

 condition; "B," cell deprived of its nor- 

 mal water. (After Bergen and Davis, 

 "Principles of Botany." Ginn & Co.) 



Figure 4. \ swamp enduring tree, the 

 Cypress (Taxodium distichtim. Rich.) 

 Note the root projections or "knees 

 above the water surface. (After Bergen 

 and Davis, "Principles of Botany. 

 Ginn & Co.) 



of different density arc separated from 

 each other by protoplasm which per- 

 mits the passage of the less dense only, 

 the less dense liquid moves in through 

 the protoplasm into the more dense 

 liquid. There would be no object in 

 here explaning this water intake if it 

 did not help to make clear the reason, 

 at least in part, for the unfavorable 

 effects of alkaline soils upon plants. 

 Figure 3 shows at "A" a root cell which 

 is in normal condition. If such a cell 

 is surrounded by a soil sulficiently alka- 

 line, water, instead of moving into the 

 root, tends to move in the opposite 

 direction— that is, it moves out of the 

 root, leaving a collapsed living cell as 

 shown at "B." It is thus iiossible for a 

 tree to be unable to get needful water 

 in too alkaline a location, even though 



