for November, 1920 



373 



How Often Does a Branch Bear Leaves? 



WILLARD N. CLUTE 



H 



(.•W often (loL-s a branch bear leaves? At first 

 i^lance this seems to be an extremely foolish cjues- 

 tion. One is inclined to say that a branch bears 

 leaves every year as long as it lives, but a little investiga- 

 tion serves to show that this is far from the truth. As a 

 matter of fact, branches bear leaves but once — during 

 the year the branches themselves were formed. We have 

 only to consider the way in which leaves and branches 

 are formed to see that this is so. Everybody is familiar 

 with the buds that stud the bare branches at the begin- 

 ning of the year and everybody knows that these buds 

 consist of numerous tiny leaflike parts, attached to an 

 equally minute stem. When the bud scales loosen in 

 Spring these minute parts soon develoj) into a leaf} 

 branch, but after these leaves have fallen no new ones 

 ever take their places. 



Everv one can call to mind, however, branches that ap- 

 pear to be clad with new verdure as often as the vernal 

 season comes round, and 'if branches do not bear suc- 

 cessive crops of leaves it may be asked where these leaves 

 come from. The answer is that shortly- after the sea- 

 son's leaves are fully spread, often as early as July, new 

 buds begin to form in the angle between the leaf and 

 stem, or, in the a.xil of the leaf, as the botanist puts it. 

 and it is this bud that produces the next crop of leaves. 

 When the old leaves fall off they leave a more or less 

 distinct scar. This is especially noticeable on the horse 

 chestnut, the hickory and the Chinese tree of heaven, but 

 may be easily found on any of the woody plants that drop 

 their leaves in Autumn. It will be noticed in examining 

 these leaf scars that the leaf has been removed by a clean, 

 smooth cut and that the wound has been carefully closed 

 with corklike tissue to prevent loss of sap. The se])ara- 

 tion of the leaf from the stem, therefore, is not an inci- 

 dental matter, but has been carefully provided for a long 

 time in advance. By the end of August and often earlier 

 a layer of brittle cells, called a cleavage plane, is con- 

 structed across the base of the leaf. Then when an ac- 

 cumulation of frost on the leaf increases its weight, or 

 when a high wind brings pressure to bear upon it, the 

 brittle cells gi\e wav :ind the leaf goes whirling to the 

 ground. 



Though a l.iranch bear leaves but once, this does not 

 necessarily mean that it is clothed with leaves for only a 

 season or part of a season. In certain evergreen plants, 

 such as the laurel, pine, spruce and fir, the leaves may 

 remain on the jilant for a long time — in extreme cases 

 as long as fifteen years. One may discover evidences of 

 this in almost any evergreen thicket. The place where 

 the growth of the branch is sto])ped by the cold each year 

 is easily discovered and it is evident that any leaves on 

 one side of this zone must be more than a year old. 



In regions of unifonu warmth and moisture the w^oody 

 vegetation often grows nearly continuously, since it is 

 never exposed to cold or drought and has no need to 

 stop and protect the growing jioints. In more northern 

 regions, however, the plants seem to have learned by 

 long experience that a season of cold follows the grow- 

 ing season and weeks before it occurs have begun to 

 prepare for it. Often all the leaves that are to ap]icar in 

 a given year are present in the winter buds when 

 these have been expanded the plrmt stops, though it ma}' 

 be in the middle of Sunnuer. The species in our flora that 

 have been derived from southern ancestors conimonl}- 

 fail to prepare for the more rigorous season and continue 

 .growing until frost nips their tender tips. 



Se\eral of the species that prepare for Winter early 

 mav take on a new growing imi)ulse late in Sinnmer and 

 thus have a sort of new Spring all to themselves. This 

 habit is very noticeable in the elms, where the tender 

 yellow-green of the new foliage is very conspicuous 

 against the darker green of the older leaves. In every 

 case, however, the new leaves spring from new stems or 

 extensions of the old one.s — never from that part of the 

 stem previously developed. 



In some instances leaves seem to s[)ring from the same 

 points year after year, as iti the dwarf branches of fruit 

 and other trees. It is possibly not widely known that 

 many of our trees bear two kinds of branches — long 

 branches and dwarf branches. Pine trees are rather ex- 

 treme in such matters, for they have not only the two 

 kinds of branches but two dift'erent styles of leaves to go 

 with them. One may find dw.irf branches in the apple 

 and pear trees as short stubs along the main branches. 

 These are usually called fruit spurs by the orchardist. 

 Such dwarf branches may produce new flowers, fruits 

 and leaves year after year, but a careful examination will 

 disclose the fact that they do not produce new leaves and 

 flowers from exactly the same place. The spur grows 

 a trifle longer each year and affords new places for the 

 leaves. The exterior of such a sjnir is usually a mass 

 of overlapping leaf scars. 



Although it is the fashion for the majorit}' of leaves 

 III live but a single season, and permitted of only a few 

 to exist for much more than a dozen years, there is one 

 most conspicuous exception in the ll'cl'n''tscliia of west- 

 ern Africa where leaves live as long as the plant does — 

 often fifty years or more. There is good reason for this, 

 however, for the plant has but two leaves. These are 

 long and broad in spite of the plant's relation to the pine 

 family and sprawl about on the soil. The peculiar form 

 and method of growth has induced the British Govern- 

 ment, in whose territory it grows, to protect it from ex- 

 termination, and thus the plants are likely to live on for 

 centuries, the best illustration to be found of the great 

 age to which the leaves of plants may attain, 



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I WILL YOU HELP SUPPRESS | 



.1 THE SIGN BOARD VANDALISM i 

 I ALONG OUR HIGHWAYS? | 



I At the convention of the National Association of | 



I Gardeners, held in St. Louis in September, a resolu- | 



I tion was adopted condemning the despoliation of the | 



I beauties of the natural scenery along our highways | 



I by unsightly sign boards. It was decided to begin | 



I a counliy-wide propaganda to arouse an indignant | 



I public sentiment against this nuisance. | 



I We invite every individual and organization inter- j 



I ested in seeing the scenic beauties along our highways | 



j protected and conserved to co-operate with us in sup- | 



f pressing this sign board vandalism. | 



If interested, address j 



, SIGN BOARD COMMITTEE | 



I National Association of Gardeners | 



I 286 Fifth Ave., New York, N. Y. | 



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