188 BOTANICAL GAZETTE [February 



is undoubtedly associated with reversed gradients brought about by unfavor- 

 able conditions of confinement. 



These changes in gradients of hairs were studied particularly in Griffithsia. 11 

 If conditions are not extreme, obliteration or reversal of the axial gradient is 

 followed by cell separation, and the death of some of the cells, the death-rate 

 being higher among isolated apical cells than among those more basally 

 situated. The cells which do not die usually proceed to grow new apical cells, 

 which are found to arise at the most susceptible end of the old cells. This is 

 usually the basal end, because the normal gradient had been reversed before 

 the cells were disconnected. Rhizoids, however, arise only on those parts of 

 the cell which have the lowest metabolic rates or lowest susceptibility. 



The general conclusion of all this work is summarized admirably in the 

 words of the author: "The facts support the conclusion that a gradient in 

 metabolic rate, protoplasmic condition, or whatever we prefer to call it, of 

 which the susceptibility gradient is within certain limits an indicator, con- 

 stitutes physiological polarity in protoplasm, and that such a gradient is not 

 an inherent property of protoplasm, but may be determined and altered by 

 external factors." 



Students who desire to repeat some of these experiments for themselves 

 will find a recent paper of interest. 18 The axial gradient may be very beauti- 

 fully demonstrated colorimetrically by the use of dilute solutions of potassium 

 permanganate. The protoplasm reduces the permanganate and takes on a 

 brown color, which appears first and deepest in the most active regions. 

 Concentrations of M/iooo to M/ 100,000 should be used for such experiments. 

 C. A. Shull. 



Biology and culture of the higher fungi. — Among recent contributions to 

 our knowledge of this difficult subject is a paper by Boyer 19 . The first part 

 deals with attempts at spore germination and culture of over 60 species, and 

 the second gives in more detail the results of his work with Morchella and 

 P sal iota. 



Jie recognizes three types of higher fungi: (1) pure saprophytes, (2) facul- 

 tative parasites, and (3) mycorhizal forms which are constantly associated 

 with certain trees. Saprophytes, he finds, grow readily on culture media, and 

 many give rise to carpophores ; while many of the mycorhizal group cannot be 

 grown in pure cultures on any of the many types of media tried. Between 

 pure saprophytes and forms which will not grow on culture media he finds 



J 7 Child, CM., Experimental alteration of the axial gradient in the alga Griffithsia 

 Borndiana. Biol. Bull. 32:213-233. 1917. 



18 ___^ Demonstration of the axial gradients by means of potassium perman- 



ganate. Biol. Bull. 36:133-147. 1919. 



x * Boyer, G., fitudes sur la biologie et la culture des champignons superieurs. 

 pp. 116. pis. 4. Jigs. 20. Bordeaux. 1918. 



