16 GREENHOUSES 



mats as late in the season; (3) in moderate 

 climates no mats or supplementary protec- 

 tion is needed; (4) the plants receive sun- 

 light during the entire day when mats are 

 not used, whereas, with single glass sash, 

 the mats have to be left on until the sun 

 is well up and then have to be replaced be- 

 fore sundown. 



On the other hand, they have several dis- 

 advantages: (i) The first cost is often as 

 much as 50 per cent, greater; (2) they are 

 heavier to handle; (3) they reduce the 

 amount of light, especially if the glass be- 

 comes loosened so that dust accumulates 

 between the layers; and (4) some users com- 

 plain that they are short-lived because moist- 

 ure collects between the layers and promotes 

 rapid decay. 



The most enthusiastic supporters of these 

 sash are those who live in climates where 

 this type of sash never need supplementary 

 protection, but where it is not safe to leave 

 single-light sash unprotected. It is but fair 

 to state, however, that their use is rapidly in- 

 creasing, even in the north. 



Temporary Sash, made of oiled paper or 

 treated cloth, are sometimes used for special 



