for February, 1921 



A67 



Plant Travelers 



WILLARD N, CLUTE 



THE casual observer finding the plants nf held and 

 wood rooted in the soil might hastily conclude that 

 organisms so fix;.'d in their places cannot move 

 about, but a closer investigation should convince him that 

 the reverse is true. Plants, to be sure, cannot move as 

 rajiidly as animals, but judged by their accomplishments 

 they appear perfectly able to spread from one locality 

 to another if given time enough. The dandelion has 

 spread quite round the earth, a feat which few animal 

 travelers have equalled though the English sparrow, the 

 rat and the mouse make a pretty good showing. 



In one important respect, however, the migrations of 

 plants differ from those of animals, ^^'hen the latter 

 move into a locality the journe\- is accomplished by their 

 own efforts and is directed by a certain amount of se- 

 lective intelligence. Plants, on the contrary, have no 

 choice as to the direction of their migrations and from 

 the time the young plant, which we call a seed, leaves 

 its parent, its movements are due entirely to chance. 

 Moreover, the animal has a greater range of adaptability 

 and is not so vitally affected by slight differences in its 

 environment. In a measure it can modify its environ- 

 ment, but plants cannot, ^^'hen they spread into distant 

 regions it is by a series of trials, the outcome of which is 

 decided by wild Nature. 



Under the circumstances it is small wonder that plants 

 produce so many more young than do animals. There 

 are a number of species that in favorable circumstances 

 may produce a million or more young, anntially. No 

 ordinary animal can equal that. When the young plant 

 attempts to lay hold of the new region in which it finds 

 itself, however, there begins a silent though deadly strug- 

 gle with wind and weather, with birds, insects and 

 fungous pests, with drouth and cold and with other plants, 

 in which it must often go down to defeat. The necessity 

 for the production of a large number of seedlings by 

 plants if they would maintain their race is thtts ver}- 

 apparent. 



Though jilants exercise no conscious eft'orts in reach- 

 ing and holding new regions, thev are often very elab- 

 orately equipped by their parents for success in such an 

 undertaking. There is scarcelv a seed or fruit that is 

 not modified in some way for distribution. Those which 

 come nearest to being without such aids are the tiny 

 specimens, but their very size is in their favor and the 

 friendly wind scatters them far and wide along with other 

 animate and inanimate dust. In this method of distribu- 

 tion they follow the example of the mosses, ferns, and 

 other flowerlcss plants whose exceedingly small and light 

 spores are carried to immense distances. In one case 

 recently recorded, fern .spores have traveled on the wings 

 of the wind for more than ten thousand miles ; from the 

 Himalayas, across the Pacific, to settle at last in Arizona. 

 Though the seeds themselves may have no means of their 

 own for distribiUion, the capsules in which they are borne 

 often give them a good start, being so constructed as to 

 shake out a few at a time when the wind is high, as in 

 the case of the poppy and snajidragon. Then there are 

 the various tumble-weeds which go rolling and bounding 

 over the wastes shaking out the seeds as tliey go 



Since the wind works for nothing, a large number of 

 seeds and fruits make use of it for transportation. One 

 grfiup trusts to parachute devices and sails upon the 

 wind often for days, coming down when the wind dies 

 out and resuming their travels when it rises again. The 



winged seeds and fruits are rather more interesting since 

 their modifications appear to have a measure of intelli- 

 gence behind them. There are some of course, whose 

 membranous outgrowths serve merely to catch the wind 

 and thus drive them onward, but the majority have the 

 wings so set that when severed from the plant thev .spin 

 round like a propeller and thus delay for an appreciable 

 interval, their descent to the earth during which they are 

 wafted to a considerable distance. 



Other currents besides the air may be used. The seeds 

 of a number of water plants, as befits their station in 

 life, are fitted with corky floats that make efficient life- 

 preservers. Others that make use of the same medium 

 for transportation put their trust in inflated chambers, 

 like the water-tight compartments of modern ships. Thus 

 eciuijijied they may float for many days. 



A \cry large number of wingless seeds have been able 

 to acqtiire wings by the simple expedient of wrapping 

 themselves up in substances that please the palates of the 

 birds. Borne on feathery pinions they seldom fail to be 

 carried long distances. The majority are enclosed in 

 hard seed-coats so that if swallowed they escape digestion. 

 Of somewhat more calculating dispositions appear those 

 fruits with hooked appendages for laying hold of the 

 clothing of passers-by, whether man or the other ani- 

 mals, and thus certainly, though often unwillingly, trans- 

 ported. To secure samples of these one has only to ex- 

 amine his clothing after passing through a weedv field 

 in Autumn. 



It is a noticeable fact that the hooked fruits are always 

 borne near the ground where animals may come in con- 

 tact with them, but that the winged fruits are usually 

 found high on the plants so that when they release their 

 hold on the parent, they have a considerable distance to 

 go before reaching the ground. The juicy fruits beloved 

 by birds may be borne at any height but it is interesting 

 to note that nearly all are borne on woody plants. 



It may be questioned whether the hard shells of nuts 

 are adaptations for distribution or whether their hard- 

 ness merely protects them from gnawing animals until 

 they get started in life. In any event they are often 

 distribtited bv small mammals who hide them away and 

 often forget or fail to return to them. There are many 

 ball-like fruits, the osage orange for example, that are 

 distributed by simplJ-V; rolling about on the ground or li\' 

 being" washed along by the floods of Winter and Spring. 

 It is possible that the distribution of nuts is largely of 

 this nature and the transportation by animals merely 

 fortuitous. 



Possibly half of the seeds with special means of dis- 

 tribution owe their dispersal to various forms of slings. 

 In practically all of these the dtying out of the tissties 

 ilevelops a tension that increases until with a sudden snap 

 the seed-pod bursts, projecting the seeds in all directions. 

 In some cases the seeds are thrown a thouand times their 

 length. The sand-box tree of the Tropics is a classic 

 example of such decrepitating ca])sules. The fruit of this 

 s])ccics is nearly as large as one's fist and bursts with a 

 loud report. The discus-shaped seeds, a little larger than 

 a coat-button are admirably shaped to sail long distances. 



The aids to the distribution of plants thus far men- 

 tioned all look toward the establishment of new individ- 

 uals at long distances from the parent plant, but vegeta- 

 tion has other methods of peopling a region with plants, 

 wherein an indixidiird, once establishctl. mav start a col- 



