174 



SCIENCE 



[ISr. S. Vol. XLI. No. 1048 



the desert perennials. These are in brief: (1) 

 roots which never penetrate the ground deeply, 

 whatever may be its character. Most cacti have 

 roots of this kind; (2) roots which penetrate 

 deeply and which have a few or no roots near the 

 surface of the ground. A typical example is found 

 in Koeberlinia, although Prosopis, also, usually 

 has roots of this type. And, finally, (3) many 

 plants have roots which are intermediate between 

 these extreme forms, and which may be said to be 

 of a generalized character. Covillea, and many 

 other species, have generalized root-systems. 



The absorbing roots of the superficial type, type 

 1, lie, for the most part, from 5 to 15 cm. beneath 

 the surface, while the anchoring roots are usually 

 not much over 30 cm. deep. Since most of the 

 roots of this type are absorbing roots, it follows 

 that most of the roots are placed close to the 

 surface of the ground. The deeply placed roots, 

 type 2, on the other hand, may lie from 2 m. to 

 5 m. and much deeper, and have few superficial 

 absorbing roots. The generalized root-systems 

 may occupy any horizon between immediately be- 

 neath the surface of the ground and a depth of 

 2 m. or over. There is apparently no differentia- 

 tion into anchoring and absorbing roots in class 2 

 and class 3. 



A study of the mean maxima soil temperatures 

 for a depth of 15 cm. and 30 cm. shows that the 

 annual swing is from 46.5° F., in January, to 

 94.5° F., in July, at the shallower depth, and from 

 39.0° F., to 87.5° F., at the greater depth. Thus 

 there is a difference at the beginning of the most 

 active growing season of 7° F., in soil tempera- 

 tures between a depth of 15 cm. and a depth of 

 30 em. The temperature decreases with depth, so 

 that as far as the records show, at depths less than 

 15 em. the maxima temperatures in midsummer 

 are greatest. 



From the striking difference in root habit and 

 from the marked difference in soil temperatures 

 which comes with variation in depth, it follows 

 that, in nature, plants having root habits of so 

 diverse a character as has been given must needs 

 be exposed to widely different temperature condi- 

 tions of the soil. 



Associated with the fact last presented is the 

 one that perennials, with different root habits, have 

 each their characteristic reaction to soil tempera- 

 tures. For example, Prosopis, with a deeply pene- 

 trating root-system, exhibits, so far as its roots are 

 concerned, active growth between temperatures 

 (less than) 15° C. and 42° C. While Fouquieria, 

 with a root-system resembling very nearly that of 



the cacti, exhibits little root growth in soil tem- 

 perature under 20° C, and the same is true of 

 Opuntia versicolor. The rate of growth increases 

 with temperature rise until an optimum is reached 

 between 30° C. and 35° C, although growth con- 

 tinues to 40° C, and above. 



Thus, to an extent not now known, perennials 

 with strikingly different root types show unlike 

 and characteristic response to soil temperatures. 

 It is thought that the difference in temperature 

 response, coupled with differences in soil tempera- 

 ture, are the definitive factors which bring about 

 the characteristic distribution in the soil of the 

 roots of the species studied. It is largely because 

 of these conditions, also, that "exposures" are so 

 important in determining the characteristic distri- 

 bution of many species, especially in arid or semi- 

 arid regions. 

 Effect of Temperature on Glomerella: C. W. 



Edgekton. 



Different species or strains of the genus Glome- 

 rella respond, differently to different tempera- 

 tures. One form, the one found on bean, Colleto- 

 triclmm lindemwfhianum, is very susceptible to 

 high temperatures, growth ceasing at about a tem- 

 perature of 31° 0., thus explaining why this form 

 is not prevalent during the hot part of the sum- 

 mer or in warm climates. The different Glome- 

 rella strains fall into several classes in regard to 

 the temperature factor. These classes are repre- 

 sented by such forms as Collectotrichum linde- 

 muthianum, CoUetotricJium lagenarmm, a slow- 

 growing form from apple, a fast-growing form 

 from apple, and Gloeosporium musarum. Nearly 

 fifty different cultures have been grown at tem- 

 peratures ranging from 14° C. to 37.5° C. 

 The Nature of Antagonism: W. J. V. Osterhout. 



As the result of his studies on permeability the 

 writer finds it possible to predict what substances 

 will antagonize each other in their action on liv- 

 ing tissues. This . opens the way to a general 

 theory of antagonism. 

 The Chemical Dynamics of Living Protoplasm: 



W. J. V. OSTEEHOUT. 



By means of electrical measurements it is pos- 

 sible to follow reactions in living protoplasm with- 

 out interference with the progress of the reaction 

 or injury to the protoplasm. It is thus possible 

 to determine the order of the reaction and to as- 

 certain whether the reaction is reversible. It ap- 

 pears in many cases that the reaction is reversible 

 up to a certain point; beyond this it is irreversible. 

 The reasons for this are discussed. 



