496 BOTANICAL GAZETTE [December 



but they are present in the leaves of C er ato phyllum ; while DeBary 

 (6) denies their presence in both genera. 



It is evident, therefore, that some writers consider as dia- 

 phragms the thick masses of parenchyma at the nodes of certain 

 plants, while others do not. The loose use of the word has led 



to much confusion, and it is necessarv to define the term. The 



diaphragm 



intervals 



from 



of plants. This definition excludes 



partitions occurring in the pith of certain trees (Juglans, etc.), 



massive 



by Wiesner and Molisch (36) to be impervious to air. Owing 

 to the uncertainty as to the exact meaning of the term, unless per- 

 forated diaphragms are distinctly mentioned, one can never be 

 sure that such structures are present in the plant under considera- 



In the discussion of the distribution of diaphragms among 

 s, no effort has been made to distinguish the reports of "per- 

 id diaphragms" from those of "partitions," because many 

 k nces to diaphragms are without descriptions or figures. 



tion. 



III. Occurrence of diaphragms 



A. DISTRIBUTION IN THE VARIOUS PLANT GROUPS 



From a study of the outline given under the heading above 

 (see p. 514), it is evident that among the angiosperms the great 

 majority of families in which diaphragms have been found are 

 monocotyledons. It cannot be said, however, that they are re- 

 stricted to this class, or that they are characteristic of certain 

 genera. I have examined representatives of various families of 

 dicotyledons with the result that diaphragms were found in one 

 species only, Myrio phyllum tenellum. In this species beautiful 

 perforated diaphragms are present at the nodes, while a second 

 species, Myrio phyllum hutnile, and a specimen believed to be 

 another species of the same genus show masses of tissue at these 

 points. Further investigations along this line are in progress. 



B. IN PLANT PARTS 



Diaphragms have been reported for all parts of plants except 

 flowers and fruits, and in the following order as to abundance: 



