Kelley — 134 — Mycotrophy 



the Hartig net, after Theodor Hartig who early described it from 

 pine. Hartig considered the deHcate net to consist of anastamosing 

 intercellular canals (Mangin, 1910:245): it had been described by 

 NicoLAi (1865) as "thickening strips", and he said that they are 

 found not only on radial cell walls but in all places where the cells 

 are not pressed together, so that a peculiar net is formed. He found 

 them in conifers and the apple-tree. Reinke (1873) also described 

 such a structure from a number of conifers, and van Tieghem & 

 DuLioT (1888), as a "reseau de soutien". In pines, Hartig-net is 

 formed of 2-3 rows of hyphae, as in Moller's P. sylvestris (Shimizu, 

 1930); Hartig net also occurs in spruce (Melin, 1921), in Podo- 

 carpineae (Berggren, 1887), and in the fern Tmesipteris (Dan- 

 GEARD, 1891). Because of mutual pressure of cortical cells, hyphae 

 penetrating between them become flattened and, branching, are 

 formed into a digitate appressed structure which Mangin (1910) 

 called a palmette. But Mangin (1898) said that there is no network 

 in the cortex but, because of pressure exerted upon them, the hyphae 

 are flattened into regularly branched layers between the cortical cells. 

 Voss & ZiEGENSPECK (1929) Said that in older plants of Betula 

 pubescens the Hartig net is digested ; and in pine it also breaks down 

 (Lewton-Brain, 1901). 



The Stele: — In general, mycelial infection of the central cylinder 

 does not occur, yet exceptions have been noted. Thus, Dufrenoy 

 (1917) found infection of all tissues in Arbutus Unedo, and in 1920 

 recorded heavy infection of pericyclic tissues of Adenostyles albi- 

 frons. Lewis (1924) found the endophytic fungus growing through 

 all the tissues of all vegetative organs of Picea and Larix; and 

 Rayner (1927:p.l00) found similar growth in Calluna stems. Masui 

 (1926&) found outer layer of pericycle in old roots invaded and in 

 rare cases the whole central cylinder, which was subsequently de- 

 stroyed. The stele of Cupania is also sometimes invaded (Waage, 

 1891). Infection of the stele was found in young roots of Lygino- 

 dendron but not in older roots by Ellis (1917); while Schacht 

 (1854) had found vascular infection of a leguminous wood from the 

 London clay as well as in living ferns and other plants ; although in 

 these cases the infection may well have been parasitic: indeed, in all 

 cases of vascular infection the endophyte may be parasitic. 



That the endophyte influences structure of the stele is a fact not 

 widely recognized, according to Noelle (1910), who said that "es 

 ist bisher nicht bekannt das ein ektotrophes Myzel die Struktur nicht 

 nur der Rindenschichten, sondern haufig auch das Zentralzylinder zu 

 beeinflussen scheint". The "normal" (uninfected) root is diarch but 



