Lecture IX — 125 — Structure 



Polygonum viviparum. According to Christoph (1921), these my- 

 corrhizae occur in ericads only in such species as Arctostaphylos Uva- 

 ursi which form coralloid mycorrhizae in humus, the fungal mantle 

 living at the expense of epidermal cells. Again, he says that such my- 

 corrhizae occur only in such species as have subterranean organs dif- 

 ferentiable into rhizome and root, and especially when, in a humus- 

 rich location, a copious branching of short-roots has been produced. 



Ectotrophic mycorrhizae are, accordingly, distinguished by an 

 exterior mantling of hyphae that have been called a "mycoclena" or, 

 when tightly weft into a pseudotissue, a "mycoderm" ; from which 

 extend hyphae into the surrounding soil. The endophyte penetrates 

 intercellularly into the epidermis, or in some sorts of plants into the 

 cortex, in the latter case forming the structure which appears as the 

 Hartig net. If intracellular infection occurs, then the mycorrhiza is 

 not strictly ectotrophic. These mycorrhizae occur on roots of woody 

 plants, rarely on herbs. 



Endotrophic Mycorrhizae: — It is evident that a diverse series 

 of mycorrhizae have been grouped under the term "endotrophic". 

 Frank (1887) included here those of ericads, which have a mantle 

 and approach the ectotrophic condition ; mycodomatia have been in- 

 cluded also; and Gallaud (1905) included mycothalli. Endotrophic 

 mycorrhizae are typically developed in all Pinaceae except the Abie- 

 tineae (which areectrotrophic) {cf. Noelle, 1910) ; in orchids, and in 

 herbs in general. 



Gallaud (1905) distinguished endotrophic mycorrhizae into 

 "series", viz. (1) Series of Arum maculatum: Mycelium at first intra- 

 cellular in the protective layer of the root, then intercellular and lodged 

 in the plasm ; arbuscles and sporangioles generally simple and without 

 very precise localization. Examples are cited from monocotyls, dico- 

 tyls, and Angiopteris. {2) Series of Paris quadrifolia: Mycelium 

 always intracellular, arbuscles or sporangioles generally composite, 

 not terminal and harboured in a definite region of the root. Certain 

 angiosperms are cited as examples ; also Araiicaria, Podocarpus, 

 Sequoia and Ophioglossum. (4) Omitting the hepatics, which are 

 his third series, the Series of orchids: Mycelium always intracellular, 

 taking the form of coils (pelotons) which sometimes remain inactive 

 (host-cells), sometimes are digested (digestion-cells). Examples: 

 orchids, Psilotum and Tamus. 



In other words, in various endotrophic mycorrhizae there may be 

 simple hyphal coils formed as in the orchids, or arbuscles and sporan- 

 gioles are developed,— the nature of which will be detailed shortly. 

 Or, it might be said that there are basidial endotrophic mycorrhizae 



