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Plants from seed sown in January were exposed to artificial 

 illumination at night, and these all made decided increases in 

 growth and seed production was delayed three weeks. A 50- 

 watt electric light bulb placed 18 inches above the plants provides 

 the illumination. During February and March the increase in 

 growth was doubtless due to the longer period of daylight at 

 this time, as well as to the artificial illumination. Although they 

 were kept in six-inch pots the plants that were sown in March 

 were 6 to 7 feet high in June and were still making rapid growth 

 until in July many were over 7 feet high and all then came to 

 maturity and died off. The mildew on these tall plants did 

 not make as good growth on the upper leaves as on the lower 

 ones; only a few scattered round patches of mildew appeared 

 on the former, although the lower leaves showed an abundance 

 of mildew. Bidens frondosa is a good vigorous greenhouse 

 plant and thrives throughout the year under greenhouse condi- 

 tions. 



Sphaerotheca is a typical ascomycete, and because all sexual 

 and asexual stages may be found in a small area, and because of 

 its availability, it is excellent material for class use. The asco- 

 carp of Sphaerotheca castagnei develops on both sides of the 

 leaves of Bidens and usually spreads in circular patches which 

 become irregularly distributed over the leaves and other parts 

 of the plant. The mildew first appears on the leaves as small 

 white specks. With a lens these specks will prove to con- 

 sist largely of conidia with a few closely appressed antheridia 

 and oogonia and possibly some very young white, spherical 

 ascocarps. Pairs of oogonia and antheridia appear almost 

 simultaneously with the conidia. Older spots will show asco- 

 carps which may be slightly yellowed; eventually these ascocarps 

 turn very dark brown and appear under the lens as glistening 

 black spheres. The spots themselves are more or less circular 

 in outline with an abundance of conidia around the margins 

 and irregularly distributed conidia and ascocarps of all ages 

 throughout the rest of the area. The mildew spreads in all 

 directions forming gradually enlarging circular patches which 

 after one week show ripe, blackish perithecia in the center 

 and numerous perithecia of varying ages over the rest of the 

 spots. The central part of the mildewed area soon turns a very 

 dark brown because of the many dark brown perithecia. Conidia 



