!>1 



The following conclusions have been inferred by me from the 

 above observations : 



1. The form of the cells which compose a conductive tissue 

 can have no importance in directing the pollen tube, though they 

 may deflect it here and there in its course. This is clear from 

 the circumstance that we have in two of the species studied, a 

 conductive tissue, the cells of which are elongated at rigJit angles 

 to the path of the tube. We must therefore conclude that the 

 guidance of the pollen tube through the tissue is due to a chem- 

 otactic stimulus, thus confirming the view of Molisch and with 

 which Longo finds agreement. In order, however, to deter- 

 mine direetion, the stimulant must, I have maintained, be dis- 

 tributed differentially, from a center toward which, therefore, the 

 pollen tube must grow. I now believe that the tgg cell is the 

 origin of this substance. 



2. The behavior of the pollen tube, whether ectotropic or endo- 

 tropic, is a purely physiological character. When the mechan- 

 ical conditions make it necessary, as, e. g., in Cnciirbita Pepo, and 

 as I have show-n in Diodia teres, the path of the pollen tube is 

 wholly endotropic ; when, however, there is a free space to move 

 in, this may be used by the pollen tube, or if the distribution of 

 the chemotactic stimulant is otherwise, the free space may be 

 avoided. By inference, the ph}"logenetic interpretation of endo- 

 tropism advanced by Treub and Nawaschin is of no further 

 importance. 



For other facts and conclusions, less relevant to our present 

 purpose, the reader may be referred to the original papers. It is 

 of no small interest that almost precisely parallel facts have been 

 brought to light independently by two different observers, and 

 that, equally independently, the same significance has been 

 attached to these facts. 



SHORTER NOTES 



Evening Primroses. — The evening primroses {Onagra or 

 Oenothera^ are the center of an unusual interest at the present 

 time because of the new species which have been seen to arise 



