Kelley — 118 — Mycotrophy 



soil, and doubtless in most if not all cases this sort of mycorrhiza is 

 associated with intermittent growth. 



Pseudomycorrhizae : — Infection of a short-root by a fungus does 

 not necessarily result in formation of a mycorrhiza, for there are many 

 cases in which the infecting fungus is a parasite. Such "false mycor- 

 rhizae" had long been observed but were named "pseudomycorrhizae" 

 by Melin (1917), who observed them on pine and spruce growing 

 in Swedish moors. The pseudomycorrhiza is thinner and simple, or 

 sometimes monopodially branched, in pine ; the hyphae are intracellu- 

 lar and penetrate even the meristem, and must be considered para- 

 sitic. Melin thought that Holler's "ectotrophic mycorrhiza" was the 

 same as a pseudomycorrhiza. Latham, Doak & Wright (1939) said 

 that under field conditions most non-mycorrhizal short-roots of pine 

 become pseudomycorrhizae, thus reducing the absorbing surface of 

 the roots and their ability to take up mineral nutrients. 



Pseudomycorrhizae are thin and lack the basal constriction that 

 marks the mycorrhiza; then, too, mycorrhizae are usually lighter 

 in colour than the mother root, at least when young, whereas the 

 pseudomycorrhiza is dark in colour. 



The Colours of Mycorrhizae: — In earlier days some attention 

 was paid to colours of mycorrhizae: Thus, Mangin (1910) cites 

 Querciis with white and rose-coloured ones, Fagus with yellow and 

 blue. McDouGALL (1914) presented a classification of mycorrhizae 

 based in part on colour, vis.: bright yellow, brown, white. Masui 

 (1926) said there are three types of ectotrophic mycorrhizae on roots 

 of Alnus firma var. Sieboldiana, — white, yellow and dark. A yellow 

 colour of the root is characteristic of mycorrhizae of potato (Magrou, 

 BouGET & Segretain, 1943). 



Two things influence mycorrhizal colour, viz. age, and the fungal 

 symbiont. In general, young mycorrhizae are light in colour, often 

 a pure glistening white ; and they become darker as they grow older 

 until they usually turn brown, although very old mycorrhizae may be 

 black. But a black pine mycorrhiza may split its sheath and produce 

 a white tip of renewed growth under favourable conditions. Or, a 

 black colour may be given the mycorrhiza by a fungus long known but 

 more recently described as Mycelium radicis nigrostrigosum, which 

 usually develops strands of hyphae from the surface. Other fungi may 

 cause other colours, as yellow, reddish or pale violet ; but as the 

 mycorrhiza grows older these colours tend to disappear. 



