OCTOBEE 17, 1919] 



SCIENCE 



363 



more or less specific inhibiting substances, 

 •which are transported to other parts of the 

 plant, also presents certain dijEculties and in- 

 consistencies. In the first place every grow- 

 ing tip must be immune to the inhibiting sub- 

 stances which it produces, yet these substances 

 inhibit other growing tips; second, in the 

 normal growth of most plants new growing 

 tips of stems usually arise from previously 

 existing growing tips : it is not their origin 

 but their later development which is inhibited ; 

 third, the correlation exists in many simple 

 plants, such for example as algse, where there 

 is, so far as we know, no mechanism for the 

 transportation of such substances through the 

 plant body; fourth, the inhibiting action is 

 not a specific function of growing tips of 

 stems for a leaf may inhibit a biid. In short 

 when we attempt to interpret the facts in 

 terms of inhibiting substances inconsistencies 

 and contradictions began at once to appear. 



The third possibility, that of a dynamic 

 change of some sort, transmitted through the 

 protoplasm, has been suggested by various 

 authors, but the problem of the mechanism 

 by which such a transmitted change produces 

 an inhibiting effect has not been adequately 

 considered. 



Most experimental work along this line has 

 consisted either in removing, or stopping or 

 retarding the physiological activity of the in- 

 hibiting tip or other part, or in physical 

 isolation of the inhibited part from its action. 

 Another method of attack upon the problem 

 which has been but little used consists in at- 

 tempting to block the correlative factor some- 

 where along its path in the intact plant.^ If 

 it is possible to accomplish this blocking with- 

 out injury to the plant and to make it tem- 

 porary, i. e., reversible, the nature of the con- 

 ditions which bring about the block and the 

 behavior of the parts of the plant on the two 

 sides of the block may be expected to afford 

 at least some basis for conclusions concern- 

 ing the nature of the correlative factor which 

 is blocked. 



The experiments briefly described below 



iMoOallum, Bot. Gaz., XL., 1905, attempted to 

 block the correlative action by means of localized 

 anesthesia and obtained results of great interest. 



were undertaken because it was believed that 

 this method of temporarily blocking the corre- 

 lative factor in its passage would prove par- 

 ticularly fruitful in plants and would afford 

 a means of testing still further the general 

 conception of physiological axiation which has 

 been formulated by one of us on the basis of 

 many different lines of zoological and botan- 

 ical evidence. 



These experiments are concerned with the 

 effect of low temperature as a block to the 

 action of the growing tip upon other parts of 

 the plant. The method of experimentation 

 consists in subjecting to a low temperature 

 some portion of the plant between the inhibit- 

 ing growing tip and the part which it in- 

 hibits, while the inhibiting growing tip and 

 the inhibiting part which it is desired to 

 isolate remain at the usual temperatui'e. More 

 specifically a portion, two centimeters or more 

 in length of the stem, petiole, runner, etc., is 

 surrounded by a coil of tubing through which 

 flows a current of water, at a low, controlled 

 temperature. In order to avoid injury, the 

 diameter of the coil is made large enough so 

 that it does not touch the plant, the portion 

 to be inclosed is wrapped in tinfoil, the space 

 between it and the coil is lightly packed with 

 damp absorbent cotton, and finally the coil, 

 together with the portion of the plant sur- 

 rounded by it, is wrapped lightly with a 

 bandag-e of dry raw cotton. In this way a 

 localized region can be maintained at any 

 desired temperature above zero with very 

 slight variation, provided the temperature of 

 the water flowing through the coil is kept 

 constant. In the apparatus used in these ex- 

 periments the temperature variation inside the 

 coil can be controlled within one degree 

 Centigrade. The plants are kept in a green- 

 house at a temperature ranging from 20° to 

 25° C, while the region surrounded by the 

 coil is kept at a much lower temperature, in 

 most experiments at approximately 3° C, 

 though in some cases temperatures as high 

 as 5° or even 6° have been found effective. 



The results of these experiments with low 

 temperature are briefly as follows : It is a 

 familiar fact that in Bryophyllum new plants 

 develop from the notches of the leaves when 



