26 MANUAL OF TROPICAL AND SUBTROPICAL FRUITS 



"25 to 26 F. Mexican varieties with new foliage injured but 

 some dormant trees uninjured ; all Guatemalan sorts with new foliage 

 badly injured and some old foliage scorched. 



"24F. Some dormant Mexicans uninjured; Guatemalan varie- 

 ties badly injured, small limbs frozen back. 



" 21 F. All Guatemalan types killed to bud ; a few of the hardiest 

 Mexicans, such as Knowles and San Sebastian, with young leaves 

 only injured." 



The observations reported to Webber showed that young 

 trees were injured at higher temperatures than older ones, 

 when the variety was the same in both cases. It was 

 also observed that trees in rapid growth were more severely 

 injured than those which were in semi-dormant condition. 

 Krome of Florida reports an opposite state of affairs. He 

 says: "At the time of the January 1918 freeze, Trapp trees 

 which had borne heavy crops and were in a hard, completely 

 dormant state suffered a great deal more injury than trees 

 which, owing to light crops the preceding season, were in full 

 growth." Possibly the trees were weakened by over-production 

 of fruit, and thus more susceptible to frost-injury. The sub- 

 ject demands further investigation. 



Webber further says: "Trees which needed irrigation when 

 the freeze came suffered rather severely, as did also trees that 

 had been irrigated three to five days before the freeze and were 

 thus gorged with water. The least injury seemed to be on 

 trees that had been thoroughly irrigated two or three weeks 

 before the freeze, and had water supposedly in what might be 

 termed the optimum amount." 



In regions subject to frosts, it is necessary to protect the 

 trees during the first two or three winters with shelters of burlap, 

 or by placing palm-leaves, pine boughs, or other material 

 around them. Frost-fighting with orchard heaters is some- 

 times practiced where heavy frosts are expected. 



A sharp frost at the time the tree is in flower may result 

 in a crop failure, although the danger from this source is prob- 



