THE AMERICAN BOTANIST. 13 



flower in a few clays. The problem that confronts the 

 the nurseryman, therefore, is whether these plants need 

 the freezing they get, in order to produce their flower 

 or whether they only need the rest which winter 

 lirings. If freezing, only, is necessar\' this can be accom- 

 plished at anytime of year. Several growers have recent- 

 ly been discussing this subject in American Gardening in 

 connection v^ith lily-of-the-valley without coming to any 

 agreement. The experience of the majority indicate that 

 freezing is necessary but others maintain that the root- 

 stocks will put up the usual amount of bloom if they have 

 had their proper rest. 



Life History of the Rusts.— The individual rusts 

 are so small that the average botanist pays little atten- 

 tion to them so long as they do not affect the particular 

 plants he is after. He recognizes them, of course, as the 

 cause of various spots and blemishes upon leaves and 

 stems, but probably never examines them unless he pos- 

 sesses a compound microscope and a desire to use it. No 

 plants, however, possess a more remarkable life history. 

 Each species not only has two or three different forms 

 but produces as man^^ different kinds of spores. 

 The wheat rust is one of the best known, and usual- 

 ly serves as an example. The first form appears on 

 the kaves of the barl:)erry forming minute cup-like objects 

 full of spores on the outside of the leaves. These spores 

 germinate on the wheat and soon produce another kind 

 of spore called the summer spore. Later in the season 

 heavier or winter spores are formed. Although the poly- 

 morphic nature of the rusts have long been known, it is 

 only in comparatively recent years that systematic efforts 

 have been made to discover the relations of the various 

 forms. At present great progress is being made by collect- 

 ing the spores of the various forms and sowing them upon 

 the plants supposed to nourish other forms of the same 

 species. Often there is no infection, but occasionally a dif- 

 ferent, though perhaps well-known, form appears showing 

 conclusively the relationship. In this wa^^ rusts and 



