Vegetation and Frost. 
359 
cold, and perhaps the most interesting are those delicate herbaceous 
annuals which look so unfitted for winter existence— Holosteum, 
Cerastinm, Laminin, Veronica, Senecio, Viola, Fumaria, etc. Even 
in the Arctic flora there is nothing protective to compete with the 
snug coatings of our feathered, furred and fleecy friends and 
Kjellman concluded that protection from injury by frost must lie 
in the nature of the protoplasm. 
Lidforss has, however, established one general characteristic 
of all these plants in winter-time which does seem clearly to be 
protective. He finds that all winter-green leaves are quite free 
from starch but contain quantities of sugar (and sometimes oil) in 
the mesophyll. In the summer these same leaves contain abundant 
starch. This they regenerate in spring and if the plants are brought 
from the open into a warm room in mid-winter, starch is also usually 
soon regenerated from the sugar. 
The only exceptions which Lidforss found were the submerged 
water-plants like Elodea, Chara, which show starch all through the 
winter. The rule obviously does not break down on proof by the 
exception, for submerged plants are in an environment which will 
not fall below zero. 
Few of these winter-plants belong to Stahl’s saccharophyllous 
class characterised by general absence of starch-formation, low 
transpiration rates and tolerance of dry soil, which lowness of 
transpiration is held to be a direct result of the high sugar-content 
of the evaporating sap of the mesophyll cells. In winter all soil is 
physiologically dry and the sugar might help to keep down the 
transpiration and avoid the evils of wilting, but Lidforss finds a much 
more direct advantage in its presence. 
He first demonstrated that the sugar in the cells does enable 
them to survive a lower temperature. This can be proved by the 
simple preliminary treatment of keeping cut leaves with their stalks 
in sugar solution (5-10% of any ordinary sugar) for a few days. 
Nerinm and Viburnum Tinus are particularly good at taking up 
sugar in this way without becoming at all wilted. 
When these sugared leaves are exposed to a frost of —7°C 
they remain uninjured, while controls that had been kept 
preliminarily alongside them in water are killed and show this by 
turning quickly brown by post-mortem oxidative changes. 
Most leaves exhibit this protective action of sugar more or less, 
the real difficulty is to get the sugar into the mesophyll cells 
Not only leaves but seedlings of Helianthus, and roots of Vicia 
