232 PLANT PHYSIOLOGY 



spores of various fungi, germinated on finely perforated films 

 of collodion or of stomata-bearing epidermis floating on 

 water or solutions of various substances, or on the stomata- 

 bearing surface of Tradescantia leaves injected under the air- 

 pump with solutions of the substances to be tested, send 

 out hyphae which grow toward and through the perforations 

 into the solution, or away from the perforations, according 

 as the substances used are attractive or repellent. The 

 attractive substances are not all nutritious, the repellent 

 not all poisonous. Osmotic and dissociation phenomena 

 may be concerned. Glycerine and gum arabic, nutritious 

 though they are, do not attract. Miyoshi and Lid- 

 forss report that the direction of growth of pollen-tubes is 

 influenced by water, oxygen, sugars, and easily diffusible 

 proteids, especially those composing and associated with 

 enzyms. All of these are present in various amounts in the 

 different parts of stigma, style, and ovary. Lidforss says 

 that the direct growth of the pollen-tube toward the micro- 

 pyle is due solely to hunger certainly a graphic expression. 

 On scattering various kinds of pollen and the spores of 

 Mucor with ovules of Scilla on moist agar-agar, Miyoshi 

 found Mucor hyphse and pollen-tubes growing toward and 

 even into the ovules. 



The meeting of the conjugation tubes of Spirogyra cells 

 could hardly occur with such regularity if it were merely a 

 matter of chance. On the other hand, experimental proof 

 that their growth toward one another is chemotropically 

 directed is so difficult that no attempts have yet succeeded. 

 It has been noticed* that bacteria are attracted to those 

 portions of Spirogyra cells which grow out into tubes. 

 From this it is inferred that some special substance diffuses 

 from the tubes. This substance may not induce the cell in 

 an adjacent filament to put out a tube, yet it may so di- 

 rect the growth of a tube already forming that the two will 

 meet. Too much reliance should not be placed on inference 

 from such evidence, however, for though the behavior of 



* Overton, C. E. tiber den Conjugationgvorgang bei Spirogyra. Ber. d. 

 Deutsch. Bot. Ges., VI., 1888. Haberlandt, G. Zur Kenntniss der Conju- 

 gation bei Spirogyra. Sitzb. d. K. Akad. d. Wigs., Wien, Bd. 99, 1. 1890. 



