46 THE AMERICAN BOTANIST 



by the union of an atom of oxyg-en from the grass with the 

 molecular oxygen in the air. Still others assert that the grass 

 has nothing to do with it, except to keep the cloth damp and 

 thus enable the bleaching process to go on, since bleaching 

 agents will not act when the cloth is dry. The books are as 

 contradictory on this subject as are the chemists. If anybody 

 among our readers really knoivs, we would be gflad to have 

 him come forward and explain for the benefit of the scientists. 



Longevity of Seeds. — Nobody seems to have definitely 

 answered the question how long seeds can live. We are as- 

 sured by the scientists that seeds found buried with Egyptian 

 mummies are incapable of germination, and we know as a 

 matter of practical experience that seeds of the common food 

 plants only a few years old can seldom be induced to grow, but 

 the occasional instances of a much longer period of viability in 

 certain seeds makes one hesitate to draw the line anywhere. 

 In a recent Kezv Bulletin a case is recorded in which the seeds 

 of a leguminous plant, Alhizda lophantha, from southern 

 Australia germinated after lying dormant for sixty-eight years. 

 The seeds of different families of plants differ very widely as 

 regards vitality. Those of the Umbelliferae or parsley 

 family, for instance, seldom grow after a few years while 

 species of the pea family (Leguminosae) have a reputation for 

 being among the most resistant of seeds. The performance of 

 the Albizzia seeds, here mentioned, quite supports this repu- 

 tation and extends the range of viability so far that few other 

 seeds seem capable of surpassing it. 



The Ascent of Sap. — How the sap ascends to the tops 

 of tall trees in sufficient amount to supply the evaporation 

 from the leaves as well as to form a necessary part of the 

 plant food, has always been a puzzle to botanists. Various 

 theories have been put forth, however, to account for it. Root 

 pressure, capillarity, a sort of pumping action in the cells of 

 the stem, evaporation and many others have in turn been tried 

 and found wanting. The latest and most satisfactory ex- 



