S o SCIENCE PROGRESS 



signs of the creeping in of those semi-mystical expressions re- 

 ferred to above. 



The facts obtained in Loeb's investigations so far have 

 appeared in a number of papers during the last two years : 

 " On the Association and Possible Identity of Root-forming 

 and Geotropic Substances or Hormones in Bryophyllum caly- 

 cinum," Science, 1916, 44, 210— n; "Further Experiments 

 on Correlation and Growth in Bryophyllum calycinum," Bot. 

 Gaz. 1916, 62, 293-302 ; " A Quantitative Method of Ascer- 

 taining the Mechanism of Growth and of Inhibition of Growth 

 of Dormant Buds," Science, 191 7, 45, 436-49; "The Chemi- 

 cal Basis of Regeneration and Geotropism," Science, 191 7, 46, 

 1 1 5-18; " Influence of the Leaf upon Root Formation and 

 Geotropic Curvature in the Stem of Bryophyllum calycinum 

 and the Possibility of a Hormone Theory of these Processes," 

 Bot. Gaz. 191 7, 63, 25-50; "Chemical Basis of Correlation. 

 I. Production of Equal Masses of Shoots by Equal Masses of 

 Sister Leaves in Bryophyllum calycinum," Bot. Gaz. 19 18, 65, 

 150-74; "The Law Controlling the Quantity and Rate of 

 Regeneration," Proc. Nat. Acad. Sci. 1918, 4, 1 17-21 ; "The 

 Law Controlling the Quantity of Regeneration in the Stem of 

 Bryophyllum," Journ. Gen. Physiol. 191 8, 1, 81-96 ; " The 

 Physiological Basis ol Morphological Polarity in Regeneration," 

 Journ. Gen. Physiol. 1919, 1, 337-62. 



The chief conclusion which Loeb draws from his investiga- 

 tions is that the mass of a tissue regenerated by an isolated 

 piece of an organism is directly proportional to the mass of 

 growth material contained in the sap or blood of the isolated 

 piece, other conditions and time being constant. The experi- 

 ments were made on Bryophyllum calycinum, which is par- 

 ticularly suitable for the purpose. When leaves of this plant 

 are isolated from the stem they regenerate shoots in some or 

 many of the nodes. When a piece of stem is cut out from a 

 plant it will form shoots from two of its most apical buds, the 

 mass of shoots regenerated being in direct proportion to the 

 mass of a leaf attached to the stem in the latter case, and to the 

 mass of the isolated leaf in the former case. 



In order to explain some other facts, namely, that as a 

 rule, only the apical bud of an isolated piece of stem grows 

 out into a shoot, and none of the buds situated more basally 

 in the stem, and how it is that the same bud which grows out 



