May 4, 1917] 



SCIENCE 



437 



a dormant bud. Besides, each of the numerous 

 notches of a leaf contains a dormant bud. 

 N'one of these buds grow out into shoots in 

 the normal life of the plant. When we cut out 

 a piece of the stem containing a node with 

 its two buds, remove the two leaves, and sus- 

 pend it in moist air, the buds of the stem 

 will grow out very slowly if at all. If we 

 isolate a leaf, and suspend it in moist air, 

 a few of its many notches will grow out 

 into shoots. When we suspend a piece of stem 

 with one node and with only one leaf attached 

 in moist air the bud on the stem opposite the 

 leaf will grow out very rapidly, but the growth 

 of shoots in the leaf will be suppressed or very 

 much retarded. The writer assumed that in 

 this case substances needed for the growth of 

 the buds in the leaf were absorbed by the stem 

 and used for the growth of its bud ; and that as 

 a consequence the buds in the leaf were pre- 

 vented from growing owing to lack of material. 

 The writer has recently carried out a series of 

 quantitative experiments which seem to make 

 this theory fairly certain and a few of which 

 shall be described in this preliminary note. 



2. According to this theory, leaves of Bryo- 

 phyllum of equal size should when isolated 

 produce in the same time, at the same tem- 

 perature and moisture, the same mass of shoots 

 from their notches. This is only generally 

 true when we compare leaves of diiierent plants 

 or of different age of the same plant. If, how- 

 ever, we compare the two leaves belonging to 

 the same node of a plant (having the same 

 size, age and history) the weight of the shoots 

 produced by the two leaves is equal within the 

 unavoidable limits of error of such an experi- 

 ment, as the examples in Table I. show. The 

 two leaves of a node will always be designated 

 as a and h. 



Leaves of Bryophyllum calycinum of equal 

 size (and from the same node) produce in the 

 same time, under identical conditions, equal 

 masses of young shoots (although the number 

 of shoots formed is generally different in the 

 two leaves). 



3. It followed, moreover, that if we diminish 

 the mass of a leaf by cutting out a piece from 

 its center while the sister leaf (from the 



V. 



Leal 



3 



)h 3 



1 



|fc 2 



2 



16 4 



5 



)h 4 



4 



lib 5 



Days Gm. 

 0.350 

 0.345 

 0.290 

 0.306 

 0.375 

 0.385 

 0.594 

 0.607 

 0.457 

 0.455 



same node) remains intact, the shoots pro- 

 duced by the two leaves (when isolated from 

 the stem) should be in the ratio of the masses 

 of the two leaves. In five leaves the center 

 was cut out while their sister leaves were left 

 intact. Both sets of leaves were supended in 

 an aquarium with their apices in water. After 

 37 days the weight of the shoots formed in 

 each set of leaves as well as the weight of the 

 leaves was ascertained and it was found that 

 each set of leaves produced shoots in propor- 

 tion to its mass (Table II.). 



TABLE II 



Leaves Dipping in Water 



The shoot production in the two sets of 

 leaves was, therefore, within the limits of error 

 in proportion to the mass of the leaves them- 

 selves.^ 



When the same experiment is made with 

 leaves not dipping in water the results are not 

 so perfect, due possibly to the fact that the 

 leaves with their center cut out dry out more 

 rapidly than the intact leaves (Table III.). 



3 Since tlie surface of the leaves is approximately 

 proportional to the mass, we must for the present 

 reserve the privilege of substituting the surface for 

 weight in the expression of the numerical relation, 

 if necessary. 



