THE AMERICAN BOTANIST 



33 



In this group belong the mycosymbiotic plants. Nobody seems 

 to know just why or how independent green plants have come 

 to depend upon fungi in this way but the habit seems to l^e 

 very wide spread and new instances of it are constantly 

 coming to light. Many, if not all, the species of orchids, lilies, 

 pinks, amaryllises, saxifrages, oaks, legumes, g-entians, heaths, 

 figworts, and conifers, and species allied to them, are believed 

 to have the habit. Some of the puzzling questions involved 

 in the distribution of plants appear to be connected in various 

 ways with such phenomena. 



Manganese and Sulphur for Plants. — In all the 

 books we are told that there are only ten chemical elements 

 absolutely needed by plants in building up vegetable substance. 

 These ten are oxygen, hydrogen, nitrogen, carbon, iron, sul- 

 phur, phosphorus, calcium (lime), potassium (potash), and 

 magnesium. It appears, however, that even these ten are not 

 all used in plant substances though their presence in plants has 

 been shown to be in some way connected with their well being. 

 It has been conjectured that those elements found in plants 

 that do not occur in plant substances are of use in promoting 

 various plant processes in which other elements are used. Still 

 other elements found in plants have long been reputed to be 

 of no use whatever and their occurrence in the plant has been 

 explained on the theory that they were dissolved in the soil 

 water and entered the plant along with other solutes. Recent 

 experiments, however, seem to show that even these may have 

 unsuspected uses. An application of manganese, for instance, 

 has been show^n to increase the crop from twenty-five to fifty 

 per cent. Since this element is not a necessary constituent of any 

 of the manufactured products of plants, its stimulating- effect 

 probably comes from the influence it has on the chemical 

 reactions between other elements. Sulphur is known to be 

 absolutely necessary to plants and it has always been assumed 

 that there is enough in practically all soils for the needs of 



