Kelley — 162 — Mycotrophy 



the various mycotrophic theories ; yet they are utterly essential to any 

 theory of mycotrophic nutrition. To formulate a theory of nutrient 

 intake and ignore the intaking apparatus is like baking a cake — with 

 the baking-powder omitted. 



Ectotrophic Intake: — It is evident that there are two very 

 distinct sorts of mycotrophy, as has been indicated from early days. 

 In the first sort, the ectotrophic (if there is indeed a true ectotrophic 

 mycorrhiza), the surface of the mycorrhiza is covered with a fungal 

 mantle from which extend out numerous hyphae that assume various 

 shapes, sizes and forms. This mechanism would seem to be suited 

 to an intake of liquid materials, — water and dissolved salts, — just as 

 Frank originally observed. Yet even among these mycorrhizae there 

 is a great difference between various sorts as briefly but well shown 

 by WooDROOF (1933) for pecan. Here the surface of the mycorrhiza 

 is in some forms covered with short setae that seem tO' have the 

 qualities of root-hairs and may function as such. 



Root-Hairs Versus Setae: — -In any report of root-hairs on an 

 otherwise mycorrhizal root, a due scepticism must be maintained 

 until there is positive proof that the structure is a root-hair and not 

 a fungal hypha. Short-roots are frequently to be observed with 

 what appears to be a firm epidermis from which extend trichomes 

 in the form of root-hairs, but on closer inspection it is to be seen that 

 the "epidermis" is composed of closely appressed hyphae from which 

 setae extend. Thus, MacDougal & Dufrenoy (1944) remark that 

 the mycelium of the endophyte of Corallorhica sends "branches out- 

 wardly through the epidermal cells of underground coralloid branches 

 in simulation of the arrangement of root-hairs." In cases of doubt 

 the material must be embedded and sectioned ; and lacking such 

 demonstration we remain unconvinced in reading any report of the 

 presence of root-hairs on mycorrhizal roots. 



Endotrophic Intake: — For the endotrophic mycorrhiza there is 

 a very dift'erent structure. There is no mantle of mycelium, no myco- 

 derm, no setae; and the only hyphae that connect the mycorrhiza to 

 the soil surrounding are the so-called communication-hyphae. If water 

 and salts are to enter the mycorrhiza they must come through these 

 hyphae or through the uncuticularized portions of the exposed root. 

 But could substances come through these hyphae? Recall that the 

 endotrophic mycorrhiza is the prevalent sort, the one by far the 

 most common, especially if we consider the functioning of the ectendo- 

 trophic mycorrhiza as in part included here. Recall also that the 



