426 



GARDENERS' CHROMCLb 



The Power of Movement in Plants 



WILLARD N. CLUTE 



THE power of motion seems to be inherent in all 

 protoplasm. So common is motion in animals that 

 we mentally associate motion with life and often re- 

 gard the less active plants as scarcely alive. Among the un- 

 observant the ability to move is relied upon to distinguish 

 animals from plants, but plants are able to move as readily 

 as animals when the necessity to do so arises. Their move- 

 ments are less noticeable than those of animals because 

 they are not obliged to move about in search of food as 

 the' latter are. As regards the ability to move about in 

 the cells, the protoplasm of plants is rather more active 

 than that of animals. In numerous plant cells the proto- 

 plasm is not stationary, but is constantly revolving or 

 streaming from one part of the cell to another. 



A considerable number of one-celled i)lants, such as 

 bacteria and the simple alg.'e, move through the water by 

 lashing it with tiny threads or cilia and in some cases are 

 scarcely to be distinguished from the one-celled animals. 

 In other algae organized into chains of cells, there is fre- 

 quently a movement of the entire filament. This is very 

 noticeable in Oscillaloria a common blue-green alga of 

 stagnant pools. Most striking of all forms of plant loco- 

 motion are those movements of certain extremely simple 

 plants known as slime-molds. These may often be ff)und 

 in Spring and early Summer on rotting logs, stumps, and 

 bits of bark, as soft slimy masses of naked protoplasm, 

 white red, or orange in- color. The entire mass of pro- 

 toplasm, which is frequently as large as or larger than the 

 hand, moves over the substratum with a streaming mo- 

 tion not unlike the way in which spilled molasses spreads. 

 It is little wonder that the slime-molds were once re- 

 garded as animals. 



A large number of plant movements are connected 

 with growth processes, ranging from the adjustment of 

 the leaves to light to the coiling movements by means of 

 which climbing plants are able '"to cling to their supports. 

 Included in tliis class of movements are all forms of nu- 

 tation or nodding so common in young plants. In such 

 cases the tip of the stem I^ends toward the earth and 

 straighten^ up, joint by joint, as the stem lengthens. 

 Climbing plants appear to get up by an exaggerated form 

 of nutation. If such plants are grown at a distance from 

 a supi^rt, the tip will bend over and then begin revolving 

 in an ever widening circle until a support is reached. 

 Should a support be out of reach the stem drops to the 

 ground after a time and the tip once more becomes erect 

 and begins a new set of circles. In the case of tendril> 

 which must often quickly grasp a support, the coiling nio- 

 tion is quite rapid enough to be easily seen. It is often 

 as rapid as the second hand of a watch. The sunflowers 

 are celebrated in prose and poetry for turning their flow- 

 ers and leaves to the sun all day, but this is an error. The\ 

 derive their names from the flower-head which resembles 

 the conventional picture of the sun. and aside from facing 

 the best light do not generally move more. There are 

 some plants, however, which do follow the sun through 

 the heavens and these are commonly known as helio- 

 tropes. It is likely that not all the plants named helio- 

 trope have the habit, however. 



No adequate explanation has ever been given of the 

 movements involved in the so-called "sleep" of plants. 

 It was once thought that such movements were adjust- 

 ments made to prevent the radiation of heat at night, but 

 this seems to be negatived by the fact that plants with 

 ''sleep" movement> are comninn in the warm tropics 



where no heat conservation is necessary. Whatever the 

 cause, the phenomenon is fairly common and may easily 

 b^ observed in the leaves of axalis, clover, bean, locust 

 and many others. The habit is found in the seed-leaves 

 or cotyledons of many plants which do not exhibit the 

 habit when mature. Strangely enough the sleep habit 

 is not confined to flowering plants but is found among 

 :he fernworts. The marsilias or water-clovers close their 

 leaflets in the same way at the approach of evening. 



The numerous compass plants have the habit of turn- 

 ing their leaves in such a way that they face roughly East 

 and West with their edges toward the sky and earth. The 

 ])rickly lettuce, a common garden weed is well known 

 for this habit. In all probability it is the increasing heat 

 that stimulates the compass plants to turn the edges of 

 their, leaves to the sun. In torrid regions a number of 

 |:lants habitually carry their leaves in this position. Other 

 movements of leaves due to heat are in the nature of 

 passive changes due to loss of water, rather than to any 

 action of the protoplasm. Of this nature are the rolling 

 of corn leaves, and the flagging of numerous other plants 

 mider a hot sun. 



The classic example of a plant with motile leaves is the 

 well-known sensitive plant of old gardens and conserva- 

 tories. In this plant the leaves droop at a touch, the 

 leaflets folding rapidly together and the wdiole leaf low- 

 ering toward the earth. Heat and other stimuli will cause 

 the plant to go through its motions and it is interesting 

 to know that the plant can be put to "sleep" by the use of 

 chloroform, .\mong connnon sensitive plants are the par- 

 Iridge-pea of sandy waysides and the Schraiikia or sensi- 

 tive rose. 



Xumerous other plant movements are connected with 

 the phenomena of flowering. In this category are in- 

 cluded the opening and closing of flowers, sensitive sta- 

 mens and stigmas, various positions assumed by the es- 

 sential organs as flowering" progresses, the nodding of 

 flowers to avoid the rain or to facilitate pollination, and 

 the changes in position that occur after the flowers have 

 faded. The movements concerned with seed dispersal are 

 for the most part not movements of living matter. In 

 a majority of cases, dryness sets the trap and pulls the 

 trigger. As the fruits dry a tension is set up in certain 

 tissues which finally ruptures 'the seed vessel and scatters 

 the seeds. 



It is well known tlmt certain insectivorous plants prey 

 upon animals, catching and devouring even such active 

 forms as flies and beetles. In some cases no motion on 

 the part of the plant is necessary, the traps being so ar- 

 ranged that the insects trap themelves. In the sundews, 

 butterworts, and Venus' flytrap, however, the plants take 

 an active part in their capture. It is true that the sundew 

 and butterwort first entangle their prey in a sticky secre- 

 tion, but then the leaves roll up to form an impromptu 

 stomach in which the insects are digested. The \'enus 

 flv tra]i, however, scorns decoys of any kind and with a 

 contrivance not unlike a steel trap on the tips of the leaves 

 manages to grasp its agile prey. 



There are at the present day but too many who im- 

 agine they have perfectly done their duty, because 

 thev are kind toward their friends, affectionate in 

 their families, inoffensive toward the rest of the 

 world. — Mac.zini. 



