Kelley — 156 — Mycotrophy 



nearly 2-4 times the normal amount depending upon the degree of such 

 development. 



The Hatchian hypothesis suffers from two grave disabilities: (1) 

 it fails to take into consideration the rooting medium of the myco- 

 trophic plant. The loci of mycorrhizae are most diverse and in many 

 cases are disintegrating organic residues, and it is rather puzzling to 

 understand how there can be a total intake of water and mineral salts 

 from a medium consisting chiefly of organic compounds. (2) The 

 Hatchian hypothesis (and all other hypotheses of mycotrophism for 

 that matter) does not make provision for an intaking mechanism. 

 Advocates of the root-hair hypothesis of plant nutrition have con- 

 sidered the root-hair in detail, and in so far as root-hair nutrition oc- 

 curs the process is fairly understood ; but advocates of mycotrophy 

 blithely ignore the structure which transfers materials from the soil 

 to the interior of the mycorrhiza, and leave one to assume that in some 

 way the substances jump in. The mycorrhiza apparently says : "Abra- 

 cadabra", and the deed is done! 



Transpiration and Mycotrophy: — It must not be lost sight of 

 that the essential concept in Stahl's hypothesis, especially in the eyes 

 of his contemporaries, lay in the relation of mycotrophy to transpira- 

 tion. To Stahl, mycotrophy was most necessary to those plants which 

 have a limited transpiration stream and accordingly obtained less 

 nutrient salt in a "normal" way. A large stream of water passing 

 through the plant and being transpired from the appropriate organs 

 would presumably leave large quantities of salts in the tissues. Recent 

 work indicates that plants which transpire for long periods with 

 little elongation of the roots take in water through lenticels, breaks 

 around branch-roots and wounds (Addoms, Plant Physiol. 21 : 109- 

 111, 1946). Plants which have a limited transpiration stream and 

 hence more difficulty in securing nutrient salts are those which have 

 "sugar leaves" rather than "starch leaves". The advantage of starch 

 formation lies in the lessened trouble in assimilation and the greater 

 ease of transpiration, while addition of sugar increases the difficulty 

 of the latter. Thus, plants which secure nutrient salts with difficulty 

 are those which do not excrete liquid water from the leaves ; and of 

 these Stahl listed a number. Stahl perhaps got his idea from F. 

 ScHWARz (1883), who said that conifers and cupressineae have the 

 leaf reduced and cuticularized, and hence have a lesser transpiration 

 stream: in these trees root-hairs are lacking and the water and salt 

 requirements are met by parasites (Schmarotzern). 



BuRGEFF (1909) adopted Stahl's views on transpiration in 

 orchids, apparently without much thought ; while he found feminine 



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