36 



plaut, and does not appear to cause a great deal of damage to 

 lettuce crops, consequently little complaint is made in regard to it. 

 We have found that this mildew appears to be incapable of living 

 over the summer season in a house which is empty for a time, and 

 becomes more or less dry. The spores, or couidia, of this fungus 

 are apparently of very little duration. It is seldom that the fungus 

 is troublesome enouo;h to call for remedial measures. 



Fig. 8. — Top burn of lettuce, char- 



Top Burn, or Tip Burn. 

 The above trouble is not caused by any organism, but is due to 

 a lack of proper conditions in the lettuce house. Top burn is 



merely a wilting of the young, tender 

 leaf extremities, which causes them to 

 dry up and turn brown or black. This 

 greatly disfigures it, and injures to a 

 considerable extent the sale of the 

 /^ -:^S^3BS^^^ys=«'^^^^^ produce (see Fig. 8). Amateurs and 

 ^v_ ^ ^^ ^^^s?^ ^Y inexperienced growers are very likely 



to have top burn. It gives little or no 

 concern however, to expert handlers 

 of lettuce crops. The whole matter is 



acterized by a browning or blackening OUC dependent UpOU the absorptlOU and 

 of the edges of the leaves in the head, ^j^^j^^ ^^ ^j^^ ^^^^^, ^^^ ^^^ ^^^^^^^ ^^_ 



gether with the conditions which govern the formation of the texture 

 of lettuce, namely, heat, light, etc. To obviate top burn, care 

 must be taken not to allow high day temperatures during, or directly 

 after cloudy days, and low night temperatures should be maintained 

 during cloudy weather. Skilled lettuce growers know the texture 

 of their plants, and what treatment they are capable of standing. 

 The temperature conditions are governed entirely by what they 

 think the plant is capable of enduring. Where a rapid growth of 

 lettuce takes place, in consequence of anj^ form of stimulation, 

 care should be taken to govern temperature conditions, especially 

 those of night temperature. Lettuce plants, like all others, make 

 most of their growth during the night, and the character or texture 

 of that growth is dependent to a large extent upon temperature. 

 High night temperature will cause rapid growth and a delicate 

 texture, and lower temperature will give rise to less growth with a 

 firmer texture. 



Chrysanthemums. 



Poiodery Mildeic (Erysiphe Cichoracearum, DC). 

 Mildew frequently shows itself to a slight extent on the leaves 

 of chrysanthemums. It is of little consequence, however, to the 



