528 MINNESOTA BOTANICAL STUDIES. 



of a young tuber is diagrammatically shown in Fig. u. The 

 cell contents of the hyphae of the tuber respond very neatly to 

 a test for glycogen given by Dr. L. Errera,* and it seems very 

 probable that this substance is a very large, if not the chief 

 constituent of the cells. Errera's test is made with a reagent 

 composed of 450 parts of water, three parts of KI and one 

 part of iodine, and he designates it as " solution lodee au ^-g-." 

 According to him, material possessing glycogen when stained 

 in this solution or when mounted in a drop of it takes on a red- 

 dish brown color, which disappears in a temperature of 50-60 

 C., but returns upon recooling. Some of the tests made on 

 Dictyoflwra tubers were with material taken from 70 per cent. 

 alcohol sectioned, transferred to water and mounted directly in 

 a drop of the reagent. 



In other instances sections that had been machine cut, stained 

 in Bismarck brown, and mounted in Canada balsam were soaked 

 in xylol to remove the cover glass and balsam, carried through 

 alcohol to water, stained for a moment in Errera's mixture, and 

 then mounted in water. In every case the reaction was sharp 

 in all particulars. 



Assuming that Errera's test is a correct one, and there ap- 

 pears no good reason for doubting it, it is evident that a large 

 portion at least of the cell contents of the tuber is glycogen. 

 Zopf , Burt f and others have associated the presence of gly- 

 cogen in fungi with the immediate need of the plant for rapid 

 growth, but there is at least a possibility that this reserve food 

 supply in the tuber is in some way connected with the economy 

 of the plant in reproducing itself vegetatively the following 

 season. Or it may be that there exists a direct connection be- 

 tween the tuber and the rapidly developing sporophore, though 

 there is no evidence that any of the supply of glycogen has been 

 exhausted from any of the tubers collected or found upon the 

 vegetative tract. If it is found upon further investigation that 

 these tubers are connected with vegetative reproduction and 

 that by means of them it is possible to artificially propagate the 

 plant, it will be of great advantage in the study of the younger 

 stages of development of the reproductive area. Hitherto the 

 rare occurrence of the plant and its allies has made the study 

 extremely difficult. 



* Leo Errera, Sur le Gljcogene ches les Basidiomycetes, 1885. 

 t Bot. Gaz. 24 : 1897. 



