245 



in which it occurs ; that it is often accompanied by an acid 

 reaction of the extract, but that in such cases the toxicity is not 

 due to the acidity as such ; that it is probably organic in its 

 nature ; and that it is absorbed by finely divided solids. As to 

 the origin of such material, it is shown that toxic properties 

 appear not only in nutrient solutions in which wheat is growing, 

 but also in pure sand when this is used as a medium for growth. 

 Similar substances appear to diffuse from soaking wheat seeds, 

 and a similar toxicity is exhibited by the washings from the 

 leaves and bark of certain trees. 



In Bulletin 40, Schreiner and Reed show that agar-agar, in 

 which the roots of wheat have been allowed to grow, soon 

 becomes injurious to these roots. Agar-agar in which maize roots 

 have grown is injurious to wheat, but not to so marked a degree 

 as that rendered injurious by the growth of wheat itself. In 

 pointing out the logical conclusion that the physiological action 

 of the used agar-agar must be due to excretion from the first crop 

 of roots, the authors call attention to the analogy between this 

 supposed excretion by roots and the well-known excretion of 

 toxic substances by bacteria. 



The importance of all this to scientific agriculture is evident 

 and the changes that these considerations may bring about in the 

 theory of soil fertility may be very profound. The beneficial 

 effects of crop rotation may be explained equally well from the 

 standpoint of the Liebig theory or of this newer one, and this 

 may explain why the phenomena of toxic excretions have so long 

 escaped serious consideration. It appears that the Liebig theory 

 has been pushed rather farther than necessary, but how far it is 

 to to be supplemented or replaced by the new conception is at 

 present only a matter of conjecture. There are enthusiasts on 

 both sides of the argument. 



W. B. MCC. 



STUDIES ON RATE OF GROWTH IN THE 



MOUNTAIN FORESTS OF JAMAICA.* 



By Forrest Shreve, Ph. D.,t 



Associate Professor of Botany, Women's College, Baltimore. 



While in residence at the Tropical Station of the New York 

 Botanical Garden at Cinchona, Jamaica, during the winter of 

 1905-06, I was engaged in making a study of the physiological 

 plant-geography of the Blue Mountain region above the altitude 

 01 * 375 metres. I have in preparation a paper embodying my 

 results as a whole, from which I wish to give here an abstract of 

 the portion relating to the rate of growth in native trees and 

 shrubs as measured in their natural habitats. 



The montane rain-forest which clothes the windward slopes of 

 the Blue Mountains in the neighbourhood of Cinchona at about 



til The Johns Hopkins University Circular, No. 3, pp. 31-37. 

 t This investigation was carried on while the writer held the Bruce Fellowship 

 of this University. 



