Lecture XI — 163 — Theories 



hypha is in effect a capillary tube of relatively great length. Now it 

 is true that water passes readily through a capillary tube, but only 

 if it is empty. The fungal hypha is not empty but filled with a more 

 or less viscous colloid protoplasm. Furthermore, in the hymenomyce- 

 tous hypha there are septae at intervals, in the soil portion of the 

 mycelium, at least, although cross-walls are rare inside the mycorrhiza. 

 (It is to be noted that MacDougal & Dufrenoy [1944] , states : "Pads 

 of material at the pores of cross-walls of hyphae . . . were observed. 

 Possible similarity of composition and functioning with sieve plates 

 of higher plants is noted.") Here there are two obstacles to the 

 passage of liquids through the "communication-hyphae", — colloid 

 and cross-walls ; and unless different physical principles can be ad- 

 duced than those which ordinarily obtain, we can only conclude that 

 the "communication-hypha" is not an efficient apparatus for transfer 

 of water and mineral salts, if it is used in that way at all. 



"Individual hyphae, as the demonstrations of Frank indicate, can 

 not suffice for extensive transportation paths" (von Tubeuf, 1903). 

 "The endotrophic mycorrhizae have only a slight independent capacity 

 for absorption as compared with the autotrophs." (Endrigkeit, 

 1932). 



Hyphae as Nutrient Conveyors: — Contrast the "communica- 

 tion-hypha" with the root-hair. The latter is constructed for intake 

 of liquids : It is a thin-walled cell-extension, relatively short and of 

 considerable diameter as compared with its axial length. It has a 

 minimum of protoplasm and contains a large sap vacuole that is so 

 constituted as to aid osmotic action. The communication-hypha is 

 the opposite to all this : Its wall is not of cellulose ; it is tremendously 

 long in comparison with its diameter ; it is densely filled with proto- 

 plasm with a minimum of vacuole, and it may even be boxed off at 

 intervals by septae. 



Obviously, the communication-hyphae function otherwise, namely 

 in bringing in of elaborated organic substance to the mycorrhiza where 

 it is dealt with in an ordinary biological way. 



Teleology in Mycotrophism: — In spite of scientists' sensitive 

 denials of teleology, the current theories of mycotrophy are decidedly 

 teleological. The mycorrhizal apparatus is represented in some sort as 

 an automat wherein the mycorrhiza drops a starch-grain in the slot 

 and takes out a dish of nitrogen compounds or of phosphorus salts. 

 It is the author's opinion that ordinary processes of biology are 

 sufficient to explain the mycotrophic reactions without attributing needs 

 of salt absorption, etc., which the higher plant seeks to satisfy ; and this 

 opinion is elaborated in the next lecture. 



