BY JOHN MCLUCKIE. 305 



The hyphae, ■when stained with methyl violet and cleared in eosinelove oil, 

 stained blue. The density of the cytoplasm of the fungus depends upon the 

 period of infection of the host-cell; numerous nuclei were present, and oc- 

 casionally what I interpreted as septa were seen. In certain cells of the outer 

 cortex and in the sheath, I found spore-like bodies which had a comparatively 

 thick wall (Text-flg. 26b). 



The hyphae never enter cells of the cortex which contain raphides. I have 

 seen immune raphide-cells surrounded by a number of ordinary cortical cells 

 infected by the fvmgus (Text-fig. 2). 



The Physiological Aspect of the Mycorhisa of Dipodium punctatum. 



The first important fact in regard to the endophytic fungus of BipocUum 

 is that hyphae from the soil traverse the sheath-cells which contain little nutri- 

 tive matter, and enter the cortex of the root by means of the thin-walled, densely 

 protoplasmic passage-cells. These cells with their thin walls and cytoplasm and 

 nutritive contents must be regarded as attractive centres for the invading hyphae. 

 Some passage-cells contain numerous straight hyphae which pass directly into 

 the cortex within. They do not coil in the passage-cells or in the smaller cortical 

 cells immediately beneath the esodermis. 



The next important fact in regard to this fung-us is that the young infecting 

 hypha enters a cortical cell and grows towards the nucleus of the cell. Groom 

 (1895) in his work on Thi-smia has pointed out that this tendency of growth 

 may be due to mechanical reasons, because the cell-currents converge upon the 

 nucleus, or to a chemotropic attraction emanating from the nucleus. It is not 

 probable that the rheotropic effect of cell-currents towards the nucleus is gTeat 

 enough to influence the direction of growth of the hyphae. The work of Miyoshi 

 on the chemotropic effect of chemical solutions upon the growth of fungal 

 hyphae, rather suggests that the growth of hyphae in a host-cell containing 

 organic compounds of different kinds may be chemotropic. Moreover it is be- 

 lieved by '-^physiologists that the nucleus is an active agent in the regulation of 

 the chemical processes accomplished in plant cells, and that around the nucleus 

 there is probably a greater concentration of nutritive or chemotropic substances. 

 The more highly nourished condition of the hyphae and the gi-eater density of 

 their cytoplasm, after a sojourn in relation to the nucleus and its surrounding 

 cytoplasm, seem to support the view of active absorption of nutritive sub- 

 stances by the fungus. The infecting hypha grows into the closest contact 

 with the nucleus, and branches and coils in contact with it. The nuclear mem- 

 brane is frequently pushed inwards by the growing hyphae. 



In uninfected cells of Dipodium there is an aggregation of small spherical 

 starch gi'ains around the nucleus of the cell. The occurrence of such a quantity 

 of starch around the nucleus suggests vigorous chemical changes; sugar is pro- 

 bably present in quantity, and this substance is known to attract fungal hyphae 

 ehemotropically, and is an important nutritive substance for a fungus. When 

 such a cell becomes infected by the fungus, the starch grains gradually disappear 

 from the cell, and always from the nuclear cytoplasmic sheath first. The dis- 

 appearance of starch suggests a process of solution which may be due to 

 enzymes produced by the fung-us or by the host-cells, but at any rate stimulated 

 by the presence of the fungus. The disappearance of the starch from the liost- 

 cell, and the more dense appearance of the hyphae, suggests absorption by the 

 fungus, and the probable synthesis of proteid or protoplasm in tlie hyphae. 



During this phase of the myeorhizic fungus, it is evidently parasitic, be- 



