tor April, 1923 



99 



The Changing World of Plants 



WILLARD N. CLUTE 



OUR. forest trees, ^ once the oldest and most ambiti- 

 ous of Nature's, experiments in the vegetative line, 

 have lons" been on the decline. Not only are there 

 fewer species in the world than formerly but there are 

 fewer individuals. In spite of extensive efforts at re- 

 foresting their numbers continue to grow progressively 

 less. Once trees seem to have covered practically all the 

 earth. They formed the dominant type of vegetation ; 

 in fact, they may have been about the only forms of plants 

 in existence for few remains of other plants of that far 

 awaj' time have come down to us. The monstrous lizards 

 and other gigantic creatures that once shared the earth 

 with them have gone the way of all things and now the 

 trees are clearly following the same road. 



In view of the changes that have taken pilace in the 

 make-up of our flora and fauna one might be justified in 

 wondering whether each species, as well as each individual 

 may not have its own very definite life-cycle which after 

 a certain period of time causes it to give way to other and 

 newer forms. It is undoubtedly true that certain forms 

 of life are more primitive than others. Such forms seem 

 but poorly equipped for the battle of hfe as it is waged 

 at present. The kangaroo and the duck-ball come to mind 

 as illustrations from the animal kingdom' and among 

 vegetables many of the catkin^jearing trees are in the same 

 categor}'. 



Since the arborescent flora is the climax of vegetable 

 activity, it is naturally most numerous as to species, most 

 varied as to form and structure, and most abundant as to 

 individuals in the warmer parts of the world where all the 

 conditions for growth are at their best, but trees are by 

 no means dependent upon especially favorable conditions. 

 The hardy 'birches, willows, and asij^ens, though greatly 

 reduced in size and abundance do not shun even the lands 

 beyond the Arctic Circle and there are a great many others 

 w^hose range is entirely outside the tropics. In the Arctic 

 regions and in extra-tropical lands generally, however, 

 the trees are outnumbered by those up-start new-comers. 

 the herbaceous plants. Time was when they appear to 

 have had no competitors but little by little these more 

 modern species have pushed in, perhaps not so much 

 crowding the others out as occupying any space their 

 diminishing numbers left vacant. But in the tropics the 

 trees still make a brave stand. The prevailing type is a 

 woodv one. It is said th:it unly one species in a dozen 

 there is hcrliace'ius. 



The trees that first inhabited our globe are now prac- 

 tically extinct. The ferns, scouring-rushes and similar 

 plants were once of tree-like proportions and those we 

 call conifers were much more abundant and widespread. 

 A few of these latter are still represented on the earth. 

 It is possible that there were not as many different kinds 

 then as now. but their modern descendants thoug'h more 

 varied in form to fit many varieties of environment that 

 have since arisen are still fighting a losing battle and are 

 being pushed .steadily down the road that leads to oblivion. 

 The end lias been hastened rather than delayed by that 

 tool-using animal, Man. who has thrown the weight of 

 his activities into the scale against them, felling them by 

 the thousands and cutting up their dead bodies to serve 

 his own jxirposes. 



That the trees lack the aggressive spirit of more mod- 

 ern vegetation is seen in the almost total inability to ex- 

 tend their present areas. There is very little of the weed 

 in the trees. A,_jew may push in where they are not 

 wante-^, „... ' ^ 8^™"P tliey hold themselves aloof from 

 such matters. The box-elder comes very near to being a 



weed in some places, the ailanthus, an immigrant from 

 the Orient, is like all immigrants fond of colonizing in 

 any convenient place and the elm and cottonwood may 

 .spring up in open places ready to contest their right to 

 the spot with all comers, but this is nearly the complete 

 list. We wonder what will kill the weeds, but as regards 

 the trees, we ask how to make them grow ! 



It is not contended that trees wall not spring up in 

 new regions adapted to their groavth, but that thev have to 

 have specially favorable oipportunities for it. Thoreau 

 long- ago showed that broad leaved forests are likely to 

 follow coniferous forests and vice versa. One mcub'ates 

 the other, as it were. Under ordinary conditions a slight 

 change mav cause one group of plants to give way to 

 another. A small difference in the moisture coutent of 

 the soil or the presence or absence of a single mineral, 

 may make possible a very different plant covering. Thus 

 the chestnut is inchned to avoid soils containing lime- 

 stone and various heaths absolutely refuse to grow in 

 them. Lo-\\'cring the moisture content of the soil may 

 cause ashes anci walnuts to replace cottonwoods and wil- 

 lows and .siauilar differences determine \\-hether red or 

 jack pine shall inhabit a given area. 



One of the most important differences in the jjlant cov- 

 ering due to varying amounts of moisture in the soil is 

 seen in the division it makes between the broad-leaved 

 and needle-leaved trees. The trees with slender leaves, 

 like the pines and .spruces evaporate water very slowly 

 and are thus able to survive and to retam their leaves in 

 either cold or dry regions. So far as the trees themselves 

 are concerned, cokl regions are really dry ones, for though 

 there may be water in the soil in Winter, the trees can 

 get none of it. When conifers and broad-leaved trees 

 inhabit the same general region, the conifers w-ill be found 

 in the driest parts. At first glance this statement seems 

 in error, for almost anybody can recall conifers that thrive 

 in wet places. In such cases the soil is probably dry so 

 far as the plants are concerned by reason of various acids 

 or other substances in the water that prevent the ready 

 absorption of moisture. Thus it happens tliat some 

 .swamps and bogs may be veritable deserts to the plants 

 that inhabit them. 



.\lthough the forest trees usuall_\- produce seed in 

 abundance, a remarkablv small number sprout and grow. 

 This does not seem to be because the seeds lack vitality, 

 Ijut because for some reason the young plants fail to find 

 encouragement in the Avorkl. It is to be noted that those 

 which have adopted light and readily distribiited seeds 

 lire those most likely to extend their territories: in fact, 

 it seems probable that without interference from man, 

 the plants with wind-distributed seeds would in time 

 supplant th.ose with other means of distrilmtion. Think 

 how much more rapidly the seeds of cottonwoods can 

 move into a locality than the seeds of the walnut and oak, 

 .Still, when conditions are propitious, even heavier seeds 

 than the walnut may move into far distant lands. This 

 is true of the coconut, whose large seeds, borne 'by the 

 sea, have penetrated to the most distant lands within the 

 tropics. But when we Consider the means of distribution 

 ]X)ssessed by the coff'ee-tree, the o.sage orange, and similar 

 species, we do not wonder that until man voluntarily 

 spread them for his own uses, they occupied a very small 

 area in comparison with some of the others. 



Our grand business is, not to see wdiat lies <limly at a 

 distance, but- to do what lies clearlv at hand. — Thomas 

 Carlvlc. 



