17 



These are divided into two families upon the basis of habit of 

 growth and method of germination. The first, Albuginaceae, 

 contains a single genus, Albugo, the species of which are known 



of which are North American. Of the latter all but one are of 

 economic importance. The second family, Peronosporaceae, 

 known as the downy mildews, contains seven genera with about 

 one hundred and ten species, sixty of which are North American 



Miss Gertrude S. Burlingham has been conducting some 

 experiments at the Garden to determine the effect of magnesium 

 salts upon plant growth. Magnesium salts in the absence of 

 calcium salts are generally considered to be toxic to plants. 

 Dr. Loew makes the statement that " Plants succumb soon when 

 placed in diluted solutions of magne 



salts c 



i thei 



,nly 





sufficient amount of calcium salts." With 

 v that the inhibitory effects noted by Loew might have 

 been due to the use of excessive amounts of magnesium, experi- 

 ments were undertaken to determine the effects of magnesium 

 sulphate in dilute solutions, using the water culture method. 

 Seedlings of abutilon, pea and corn about 3 cm. long were used. 

 They were suspended over the mouth of beakers either through 

 holes in paraffined cork, or from glass rods. Growth was 

 measured for the first 168 hours. The magnesium sulphate 

 solutions were made up with distilled water and chemically tested 

 Kahlbaum salts. In each series seedlings were grown in 

 distilled water as a control. From the results obtained these 





: that 



vith c 



,vith r 



ion begins, this dilution varying with the type of seed- 

 at from this point there is a gradual increase in stimula- 

 1 each successive dilution until a maximum is reached 

 o the control ; and that the 



'ond which the growth decreases 

 ility of seedlings grown in proper dilutions of magnesium su 

 ite is greater than in seedlings grown in distilled water, 

 rwo notable contributions to fossil botany by Dr. Arthi 



