346. PHYSIOLOGY OF NUTRITION. 



V. TR ALLOCATION" OF PLASTIC SUBSTANCES. IN 



PLANTS. 



138. Experiments with Germinating Pollen^ Grains. 



The observations and experiments which we have made on the 

 behaviour of nitrogenous and non-nitrogenous substances in plants 

 have already made us acquainted with a large and varied range 

 of facts bearing on the migration of substances in the vegetable 

 organism. We will now proceed to treat the subject of translo- 

 cation more fully. We first select for examination pollen grains. 



We first prepare a small moist chamber, by cutting a frame 

 out of not too thick cardboard, making the hole in the middle 

 somewhat smaller than the cover-glass to be employed. After 

 being thoroughly soaked in water, this frame is laid on a slide. 

 We now place on the cover-glass a drop of the fluid in which the 

 pollen grains are to be germinated, add the pollen, taken from 

 ripe anthers, and then with a rapid movement reverse the cover- 

 glass. It is laid on the cardboard frame with the drop down- 

 wards, and the germination of the pollen grains can now proceed 

 in the hanging drop. We have only to take care that the cham- 

 ber is kept well supplied with water. 



The pollen grains of Alliums, of Tulipa Gesneriana, and of 

 Narcissus poeticus germinate very readily, according to Stras- 

 burger, when they are laid in a 3 per cent, solution of cane-sugar 

 in spring water, and I have myself obtained very beautiful results 

 with the pollen of Allium Victoriale. I transferred some pollen 

 grains to a hanging drop of spring water, and others to a 3 per 

 cent, solution of sugar. At a temperature of 18 C., or 19 C., 

 and in darkness, a development of pollen tubes was already 

 observable in the course of two hours, and two hours later the 

 pollen tubes had grown considerably. In the sugar solution a 

 larger number of pollen grains germinated, and longer pollen 

 tubes were formed than in the spring water. That the germina- 

 tion of the pollen grains must be associated with a transference 

 of material is at once apparent, since, in the development of the 

 pollen tubes protoplasm of course and reserve substances pass 

 over from the pollen grains into the pollen tubes. Since the 

 formation of pollen tubes takes place better in the solution of 

 sugar than in water, it is probable that sugar absorbed from out- 

 side can be utilised as food by germinating pollen grains. 



