19 io.] Time of Cutting Lucerne. 305 



and investigations by Lidforss, a Swedish botanist, have 

 suggested an explanation which appears to account for certain 

 phenomena which were previously inexplicable, e.g., the 

 effects of late spring frosts in comparison with more severe 

 frosts earlier in the season, and the reason for the beneficial 

 effect of "hardening off" plants raised under glass. 



The work of Lidforss in this direction is described in Die 

 Wintergrune Flora (Lunds Univ. Arsskrift, Bd. II., No. 13, 

 1907), which is reviewed by Mr. F. F. Blackman in The New 

 Phytologist (Vol. VIII., Nos. 9 and 10). The investigations 

 were made on the plants which remain green through the 

 winter in South Sweden, and established one general charac- 

 teristic of all these plants which appears to protect them from 

 the effects of frost. This is that all winter-green leaves are 

 quite free from starch, but contain quantities of sugar and 

 sometimes of oil in the mesophyll. In the summer these same 

 leaves contain starch, which is in the spring regenerated from 

 the sugar. 



The presence of this sugar in the cells has been shown to 

 enable the plants to survive a lower temperature, and, accord- 

 ing to Lidforss, the conversion of sugar into starch explains 

 why it is that a plant which has survived the profound and 

 prolonged cold of winter may be killed by a sharp night 

 frost in early spring, especially when the night frost is 

 preceded by a spell of bright sunny radiation. A succession 

 of warm days in spring causes the disappearance of the pro- 

 tective sugar and the regeneration of starch in the plant, and 

 it is this that makes the plant susceptible to cold. This theory 

 is borne out by the observation that it is the well-sunned south 

 side of evergreen trees like Ilex and Taxus that suffer in such 

 weather, and that here the sugar has gone, while the shaded 

 north side of the tree still keeps its sugar and is uninjured 

 by the spring frost. 



Lucerne is usually cut for hay or green fodder just before 

 coming into flower. An American correspondent, Mr, Joseph 

 E. Wing, has pointed out that lucerne 

 Time of Cutting should never be cut before certain small 

 Lucerne. shoots or buds have appeared at the 



base of the stems near the surface of 

 the ground. If it is mown off before these shoots appear. 



