July 27, 1900.] 



SCIENCE. 



145 



secondary epitropism, and the ready rooting of 

 cuttings of the grape and the common currant 

 are equally familiar examples of secondary 

 epitropism resulting from wounds and contact 

 with moist earth. The Banyan tree presents a 

 remarkable case of spontaneous secondary epi- 

 tropism. Pseudo-branches of this strange tree, 

 or branches which seem to have become epi- 

 tropically surcharged, begin a rapid growth 

 toward the earth, perhaps aided by gravitation. 

 When the distal end has reached the earth true 

 roots spring from it and penetrate the soil, and 

 a new tropaxis is formed immediately above 

 them. Above the tropaxis the shaft assumes 

 a fully apotropic condition and sends forth 

 branches some of which repeat the process de- 

 scribed until the added shafts form a vitally 

 united grove. 



The tropic balance is so stable in some plants, 

 the oaks and walnuts for example, that it is 

 diiiicult if not impossible to produce in them 

 either secondary epitropism or secondary apo- 

 tropism. Therefore, the forester propagates 

 these trees only from the seed. In other 

 plants, however, the tropic balance is so un- 

 stable that propagation is readily accomplished 

 by cuttings and layers, success in these cases 

 being due to secondary epitropism. In the 

 case of cuttings the fragments of apotropic 

 branches which are used for the purpose become 

 the main stems of the new plants, a new tropaxis 

 forming in each just above the end which is in- 

 serted into the moist earth, and whence the 

 new roots spring. It is an interesting fact, as 

 illustrated by the grapevine and the common cur- 

 rant bush that those plants which most fully and 

 readily manifest secondary epitropism as a con- 

 sequence of wounds seldom manifest it spon- 

 taneously. So persistent are cuttings of the 

 currant bush, for example, in producing roots 

 when inserted into moderately warm, moist 

 earth, that they do so even when otherwise 

 subjected to wanton violence. As a result of 

 one of my experiments when the distal or upper 

 end of the cutting, instead of its proximal or 

 lower end was inserted into the soil, roots and 

 a new tropaxis were produced there as they 

 were at the proximal end of those which were 

 not reversed ; and branches sprang from the 

 axillary buds, as they did in the other cases. 



Examples of special epitropism and apotro- 

 pism are seen in the epitropic curve of the pe- 

 duncle of nodding flowers and the subsequent 

 erection of some of them with the seed-laden 

 ovary against gravitation, under the influence 

 of fertilization of the ovules. The Western 

 Primrose, Dodecatheon medea is a good example 

 of this kind. Special epitropism alone, under 

 the same influence, is seen in the laying of its 

 fertilized ovary upon the ground by Cyclamen 

 Europoeum, and in the thrusting of its fertilised 

 ovary beneath the soil by the common peanut 

 plant. 



As a rule, the growing parts of every plant, 

 except its tropaxis, is under the influence of 

 either epitropism or apotropism, but other parts 

 of some plants are also neutral or atropic. This 

 condition exists in the slender organs called 

 runners such, for example, as those of the 

 strawberry above ground and the so-called 

 stems of the potato under ground. The straw- 

 berry runner begins its growth just above the 

 tropaxis, assumes a horizontal position, in- 

 creases only at the terminal point and shows 

 no tendency to differentiate in form or either 

 to rise or enter the soil until it has reached con- 

 siderable length. Then suddenly both epitropic 

 and apotropic action takes place in the terminal 

 cells which results in a new and perfect plant, 

 rooted in the soil and becoming wholly independ- 

 ent by the withering of the runner from which 

 it sprang. The function of the runner was that 

 of a temporary vehicle for the dispersion of the 

 species and purveyor of primary subsistence for 

 the new plant. Among the ordinary roots of 

 the potato plant atropic underground runners 

 are produced at the distal end of each of which 

 the potato, a tuberous branch having embryonic 

 buds, is formed. In these buds apotropism is po- 

 tentially developed but temporarily suspended. 

 The function of these runners is that of one 

 method of propagating the species and the 

 storing of subsistence for the future plants. 



It need not be mentioned that the foregoing 

 condensed notes contain the statement of no 

 new fact or principle, but I am confident from 

 my former use of this method of presenting the 

 subject that they possess some educational 

 value. I also claim that the special terms I 

 use are more expressive and convenient than 



