1914] 



SXOW— DIAPHRAGMS OF WATER PLANTS 



5°5 



VI. Function of diaphragms 



A. MECHANICAL 



I. 



m 



To resist strain. — Schwendener (30) considers diaphragms 

 to be girders; Haberlandt (15) and Le Blanc (17) agree with 

 him, but believe strengthening to be only one of their functions. 

 This is probably true. If certain species of Jttncus with nodose 

 stems and leaves be compared, 

 it will be seen that those forms 

 having firm, stiff outer walls 

 have a smaller number of 

 cross-partitions than have 

 those with softer walls. 



2. Support of cross-bundles. 



Leitgeb (18) , Duval-Jouve 

 (9), DeBary (6), and Sauva- 

 geau (25) definitely state that 

 diaphragms are for the sup- 

 port of cross-bundles. Le 

 Blanc (17) 



c 



Fig. 7. — Scirpus valid us: 



longitudinal 



assigns it as one 



section of stem: diaphragm varying in 

 thickness; cross-bundle (*) at edge of dia- 

 phragm establishing connectioi^L/vvith a 



of their functions Where longitudinal bundle beyond section; cells 



cross-bundles occur there 

 can be no doubt as to the 



stippled to distinguish from spaces; h, cut 



arms of cells; X 



JfrO. 



value of such support. It cannot be assigned as a function of all 

 diaphragms, however, because non-vascular diaphragms appear to 

 be characteristic of certain plants. 



B. TO PREVENT THE ENTRANCE OF WATER 



Goebel (13) believes that diaphragms are of use in keeping 



water from entering broken parts, 



stating 



that it takes 



great 



pressure to infiltrate the air passages. It is quite probable that 

 the small size of the perforations in the diaphragms prevents the 

 entrance of water against the pressure of the contained air. The 

 fact that, in order to force killing fluids into the tissues of plants 

 with diaphragms or with small intercellular spaces, it is necessary 

 to exhaust the air with a pump indicates the difficulty with 

 which water penetrates small openings against air pressure. Thi> 



