Lecture XII — ^179— Mycotrophic Phagocytosis 



Conclusion: — The explanation of these phoenomena remains for 

 the future. Certainly there is an underlying cause. Meanwhile, certain 

 facts may be pointed out. 



(1) It is already established that there is a difference between the 

 included content of stele and cortex. MacDougal & Dufrenoy 

 (1943) state: "The pericycle and endodermis layers in the root 

 mark the boundary between two contrasted t}'pes of tissues ; those 

 in the stele rich in phosphorus linkages which may be described 

 as energy-rich, and able to counterbalance the oxidase activity, 

 and those in the cortex, relatively poor in such linkages, and 

 rich in catechol and in catechol oxidase. Fungi . . . never transgress 

 beyond the endodermis into the stele." Further, these authors state : 

 "Oxidase activity seems to be higher in the cortex of the pine root 

 (whether previous to mycorrhizal infestation or after) than it is in 

 the stele. Such a difference should play a role in controlling selective 

 permeability : anions, with their negative charge, should be carried 

 from the site of higher activity, to that of the lower. The tissues of 

 the stele, from their meristematic stage, maintain a low oxidase level, 

 by retaining a high level of phosphoric complexes, acting as dehydro- 

 genases. This condition enables them to trap such anions as (H0PO4) 

 or (HPOJ". 



(2) Another fact is, that the hypha which penetrates into the cor- 

 tex develops branches at a certain point to form an arbuscle. Such 

 proliferation is ordinarily the result of introducing an hypha into 

 an hypertonic solution of ions. We may note that Burges (1939) 

 had already noticed that during early stages of infection hyphae are 

 capable of further growth but that as histological changes become 

 apparent the fungus gradually loses its vitality. "The intracellular 

 arbuscles cannot be interpreted as assimilatory organs, since they 

 are digested as they form and show no indication of hyphal develop- 

 ment from their terminal branches, but rather as proliferations 

 induced by the growth-promoting stimuli of the cell-sap" (End- 

 RiGKEiT, 1937). VuiLLEMiN, in reviewing Galea ud's work, said 

 that arbuscles are less a characteristic production of the endophyte 

 and more a result of the reaction of the host-cells to invasion 

 by a foreign body. Magrou (1939) saw incipient arbuscle for- 

 mation with endophyte of Arum, on addition of aneurin. Demeter 

 (1923) had found with endophyte of Vinca that peculiar stuntings of 

 growth, called forth by different concentrations of sugar and special 

 sorts of sugar, recall arbuscle formation. 



