Orchid Mycorrhiza. J. Ramsbottom. 53 
of the genus. The latest worker is McLennan* who used Lolium 
perenne for her researches. The fungus is far more common in 
the genus than has hitherto been thought, and it is remarkably 
constant. Every seed examined (169 of L. temulentum and 115 
of L. perenne) showed infection. The fungus is endophytic, 
occurring within the cells. It is present in the embryo sac at, 
or immediately after, fertilization: thus there is a material 
difference from what happens in orchids and Calluna. The 
fungus increases in quantity at the expense of the nucellus and 
the cells of the carpel wall. As the endosperm is formed the 
fungus is absorbed as a source of food supply for the developing 
embryo. The ovum is infected before any divisions have taken 
place in it. 
The hyphae already in the very young embryo follow the 
development of the stem-apex and remain localised in their 
growth until germination takes place. The growth of the fungus 
keeps pace with that of the plant: the hyphae, however, are 
mainly restricted to the growing apex, but can be seen extending 
for a short distance down the stem. Even at this stage the intra- 
cellular nature of the fungus can be demonstrated. Some of the 
parenchymatous cells of the grass are invaded and used as a 
food supply by the hyphae. When the inflorescence is formed 
the fungus is especially abundant at the base of the carpels. 
The cells so affected do not increase in size, and are only to be 
distinguished from normal unaffected cells by their different 
staining properties. It is not till the ovule is well advanced that 
any great increase in the fungal partner takes place. The fungus 
has not yet been isolated}. It has been suggested that it is 
probably a degenerate member of the Ustilagineae (Smuts) or 
of the ergot type. The former would seem the more likely. 
Smuts attack grasses very generally and often it is the flower 
that is infected and later the seed, and thus the whole plant. 
On general grounds it would appear that the line of develop- 
ment to the stage found would be the gradual subjection of a 
parasitic fungus such as Ustilago rather than the further de- 
velopment of a typical mycorrhiza. An examination of Lolium 
roots shows that no typical endophytic fungus is present—in 
fact these are peculiarly absent in the Gramineae, though re- 
corded by Schlicht for Holcus lanatus and Festuca ovina and by 
Tubeuf for certain moorland grasses—and the area of infection 
seems limited to the region of the stem apex. Thus, though it 
would appear at first sight that the progress of evolution had 
* E. McLennan, The endophytic fungus of Lolium. Part I. Proc. Roy. 
Soc. Victoria, xxx11 (N.S.), pp. 252-301 (1920). 
+ Fuchs (Hedwigia, L1, pp. 221-239 (1911)) claims to have proved that the 
fungus is a species of Fusarium. 
