§2] UPON THE DIRECTION OF GROWTH 341 



by a fine needle point. The solutions were injected into the 

 leaf of Tradescantia, spores were sown upon its stoma-bearing 

 surface, and the whole was kept in a moist chamber. If the 

 solution was attractive, the growing hyphse penetrated into the 

 stomata, whereas in the absence of the solution they showed no 

 tendency to do so. Similarly, spores sown on the perforated 

 plate sent hyphse downwards through the holes when the plate 

 was floating on attractive solutions, but not otherwise. Mole- 



FiG. 94. — Upper figure : Piece of the under side of a leaf of Tradescantia discolor 

 injected with 2% ammonium chloride, and sown with spores of Mucor stolonifer. 

 The young hyphse show chemotropic turnings, and have eventually penetrated 

 into the stomata. Drawn 27 hours after sowing the spores ; magnified 100. Lower 

 figure : Penicillium glaucum growing on a leaf of Tradescantia, which has been 

 injected with a 2% solution of cane sugar. The hyphs have branched, and the 

 branches have penetrated into the stomata. Drawn 25 hours after sowing the 

 spores ; magnified 70. (From MrroSHi, '94.) 



cules diffusing out from the solution through the openings 

 determine the direction of the growing hyphse, so that from all 

 directions hyphse grew radially towards the openings in the 

 membranes (Fig. 94). 



To prove that the result gained was truly chemotropism, 

 and not something else, a series of experiments was made. 

 That it was not a response to gravity was shown by sowing 

 the spores below as well as on top of a leaf ; that it was not a 

 response to light or moisture was shown by keeping the cult- 



