42 



CELERY CULTURE 



purposes. The construction of cold-frames is the 

 same as for temporary hotbeds, except that no 

 manure or other heating material is provided. Cold- 

 frames are covered by means of ordinary hotbed 

 sash, but white cotton cloth or light canvas may be 

 substituted for the sash. The same methods of 

 handling recommended for a hotbed apply to a 

 cold-frame and thorough ventilation should be main- 

 tained on bright days. Plants grown under glass 

 must be gradually hardened before time for plant- 



s 



>ROLLER 



FIG. 13 — CROSS-SECTION OF COLD-FRAME WITH MUSLIN SHADE 



ing in the garden or field. Hardening is accom- 

 plished by increasing the amount of ventilation and 

 exposure to sun and wind from day to day, until 

 finally the covering may be left off entirely, but 

 should be kept ready for use in case of severe cold 

 or frosting. The partial withholding of water will 

 assist in the hardening process, but great care 

 should be taken that the plants do not become 

 severely checked in their growth. The object 

 should be to produce a thrifty plant, well accli- 

 mated, and ready to withstand the shock of trans- 

 planting. 



Sterilization of Soil for Seed-bed. — Weeds are 



