"5 



continue to develop along with the production of perithecia, 

 though in older spots the production of conidia diminishes until 

 finally a diseased area shows little but ripe perithecia, very few 

 conidia and very little of the mycelium remaining. 



The growth of the mildew on greenhouse plants started in all 

 the cases observed on the upper surface of the leaves, the mycelia 

 appearing later on under the surface. None of the younger 

 spots on the under surface of the leaves were independent of 

 the mildew on the upper surface; it was always possible in the 

 spots examined to trace the mycelium connecting the areas of 

 mildew on both upper and lower leaf surfaces. Between Novem- 

 ber and May the mildew grew most abundantly on the upper 

 surfaces of the leaves and in many cases during December, 

 January and February there was no growth of mildew on the 

 under surfaces of the leaves. In May and June there was 

 abundant growth on both sides of the leaves, but after this 

 period the mildew grew most abundantly on the under leaf 

 surfaces producing no ascocarps on the upper parts. 



For classes in mycology Sphaerotheca should prove to be a 

 very desirable type, since one may plan to have it in vigorous 

 growing condition for study at any specified time of the year. 

 From the time of sowing the seed of the host plant to the time 

 when ripe perithecia may be produced varies from five to eight 

 weeks according to conditions. 



Columbia Untversitv, New York. 



BOOK REVIEW 



Schaffner's Field Manual of Trees* 



Another book to add to the many reflecting the present interest 



in nature study and helping increase such interest, this little 



manual is both convenient and very usable. There are keys to 



the trees in the summer condition based chiefiy on leaves; in 



the winter condition based on twigs and buds; to the fruits 



and a general key based on both leaf and fiower characters. The 



last key seems unnecessary. The keys are simple and easily 



followed through to the genera. Under these are keys to the 



* John H. Schaffner, Field Manual of Trees, 3rd Edition, 154 pp., R. G. Adams 

 and Co. Columbus, Ohio, 1926. $1.50. 



