MacDougal: tubers of isopyrum biternatum. 513 



but dissolve on boiling, and are dissolved with difficulty by con- 

 centrated solutions of chloral hydrate, and may be regarded 

 as of a waxy nature. 



The tubers as well as the roots of I. biternatum are often 

 thickly invested with a non-septate mycelium which penetrates 

 the outer layer of the cortex by means of haustorial branches 

 (Fig. 8, PI. 29). Only in rare instances has the tuber been 

 found to have been more deeply penetrated by the filaments, 

 and in the many thousands which have been examined none 

 have shown indications of injury from animals. The tubers 

 have a pungent, slightly bitter taste, and the presumption seems 

 entirely warranted that the tannin in the cell sap or the oily 

 substance in the outer tissues may serve as a means of pro- 

 tection. 



A lot of tubers obtained October 10, 1894, weighing 2.8 grams 

 gave .505 grams residue when dried over a water bath at 100° 

 C. for 24 hours. A second lot taken from the soil April 11, 

 1895, weighing 8. 74 grams gave 1. 923 grams of residue and 6. 817 

 grams of water. An ether extract, using the Soxhlet appar- 

 atus, of the residue of the first lot amounted to 3 mg. 



Water cultures. Several small plants not yet a year old were 

 placed in water culture jars filled with a solution of nutritive 

 salts in river water on October 15, 1894. These plants lived, 

 bloomed and sustained normal appearances until June, 1895, 

 although no doubt considerably weakened since they were 

 unable to form perfect seeds. In order to furnish these plants 

 with a normal degree of root temperature the culture jars were 

 imbedded in the soil of a box 20 cm. x 20. cm. x 1 meter. The 

 soil in the box received the usual daily watering of the green 

 house. The new water roots formed on these plants produced 

 a lessened amount of mechanical tissue and developed only 

 rudimentary root hairs. In several instances these roots began 

 to show evidence of the thickening usually preliminary to the 

 formation of tubers. 



Recapitulation. As a summary of the foregoing it may be 

 stated that: 



1. The tubers are formed by an excessive development of 

 the pericycle which may begin contemporaneously or follow- 

 ing the formation of the secondary tissues of the root, and that 

 the consequent enlargement is accompanied by an enforced 

 tangential development of the cortex and endodermis and a 

 radial development of the cambium. 



2. A compensation for the low value of the mechanical ele- 

 ments in the elongated tubers is furnished by the habit of 



