186 



The Plant World. 



connected with Africa in Mesozoic times by a land bridge, which 

 apparently was not wholly lost until the beginning of the Ter- 

 tiary, are still maintained by him, and are now brought together 

 with additional material, in a work published by Kngelmann on 

 Archelenis (the bridge just referred to) and Arehinotis (the an- 

 cient Antarctic continent). The need of such a bridge has been 

 keenly felt by students of distribution, but if its aid is invoked 

 to account for the present occurrence of certain closely related 

 species in South Africa and the Southwestern United States, 

 which are not found elsewhere in the world, it appears that in 

 these cases, at all events, there has been a marvelous pertinacity 

 in the maintenance of biological as well as morphological char- 

 acters since the early Tertiary. 



Lidfuss, in a biological study published by the University 

 of Lund, discusses the relation to cold of plants that remain green 

 through the winter. In winter the leaves of such plants — at any 

 rate in Scandinavia and northern Germany — are destitute of 

 starch, its place being taken by sugar. In southern Sweden 

 starch begins to be formed about the beginning and middle of 

 April, and is found in the leaves until fall, being replaced again 

 by sugar in the winter. To prove that the sugar is protective 

 the author fed solutions of various kinds of sugar to different 

 plants and subjected them, with control plants, to low tempera- 

 tures. It was found after thawing that individuals fed with sugar 

 were much less injured than those not thus fed. From various 

 data the author concludes that sugar protects the protoplasm 

 against death by freezing, in that it hinders the "denaturing" 

 of the albuminoid bodies which takes place when it is not present. 



Experiments of Apelt, reported in Beitr. zur Biologie der 

 Pflanzen, go to show that potatoes are capable of being "edu- 

 cated" to endure adverse temperature conditions. Tubers of 

 the Magnum bonum variety, which were kept four weeks in a 

 warm room, at a temperature of 22.5 degrees, were afterward 

 killed by freezing at — 2.14, but if tubers of the same variety 

 were kept at zero in an ice chest for four weeks, death did not 

 ensue until a temperature of — 3.08 was reached. Kept at inter- 

 mediate temperatures the critical point was between these ex- 

 tremes. Different varieties of potatoes were found to deport 



