﻿BOTANICAL GAZETTE 



present having an effect on germination. He further adds that 

 microchemical tests of the papillae on the stigma showed no sugar 

 or starch present, but an oily emulsion such as was found in the 

 pollen. His general conclusions are as follows: 



From these observations it appears that the stigma secretes nothing that 

 has any effect on germination or the direction of the pollen tube. The behavior 

 of the stigma in the experiments at least indicates that its function in the 

 germination of the pollen is to regulate the water supply. 



Confirmation of these results is very much to be desired, as the 

 experience of other workers in the case of various other species of 

 plants is quite contradictory. The stigma in most plants has 

 a secretory function; the amount of this secretion and its chemical 

 composition will very probably vary to some extent with the 

 amount of water absorbed by the roots, and with the relative hu- 

 midity of the atmosphere, but from the morphological structure of 

 the style and stigma it is extremely improbable that there is any 

 special mechanism for controlling the water supply. 



Jost (2) germinated pollen grains on starch paste made with 

 only one or two parts of water, and also on parchment paper soaked 

 with a sugar solution. This, it must be admitted, seems a more 

 natural method of germinating the grains than immersion in a liquid 

 medium, and resembles closely the condition found on the surface 

 of the stigma. It has the drawback, however, of being more diffi- 

 cult to observe under the microscope. His general conclusions are 

 as follows. He finds that germinating pollen grains may be placed 

 in three classes: (1) those requiring nothing but water for germi- 

 nation, much mineral matter being injurious; to this group belong 

 grasses, which can only germinate in minute quantities of pure 

 water; (2) those requiring a very dilute solution of a definite chemi- 

 cal substance which is contained in the stigma; in a few cases this 

 substance is levulose, in others organic acids, but in most cases it 

 is unknown; (3) those which germinate only in a sugar solution of 

 definite concentration. 



According to Pfeffer (i), certain pollen grains will germinate 

 only in the stigmatic fluid. Molisch (i) ascribes the curving of 

 the pollen tube to the stigma to a chemotropic reaction. He adds 

 further that pollen tubes curve toward water poorer in oxygen. 



