XXX. A CONTRIBUTION TO THE PHYSIOLOGY 



OF THE EOOT TUBERS OF ISOPYRUM BI- 



TERNATUM (RAF.) TORR AND GRAY. 



D. T. MacDougal. 



Isopyrum biternatum is found in North America northward 

 from Florida and Kentucky and eastward from the Rocky 

 mountains. It reaches its best development in a moist leaf 

 mould or coarse sandy alluvial soil on northern slopes and 

 shaded ravines near the margin of deciduous forests. The vege- 

 tative body of the plant consists of a thickened branching, 

 woody perennial rhizome with closely crowded internodes, 

 from which depends a dense tangle of fibrous roots. Arising 

 from the rhizome are a number of annual smooth, slender stems 

 11 to 20 centimeters in height, on which are borne the 2 or 3 

 ternately compound leaves, and the axillary (Gray XV.) flowers. 

 The roots penetrate the soil to a depth of 10 or 15 centimeters 

 and to an equal distance laterally. They are characterized by 

 Asa Gray (III) as "thickened here and there into small tubers." 

 The rhizomes die away in the older portions as they extend in 

 length, so that the attached roots may attain an age of two or 

 three years. A few biternate leaves in a functionally active 

 condition are present during the entire winter; the seasonal 

 vegetative period begins when the soil reaches — 5° to 3° C., and 

 continues 80 to 110 days — March- June — according to the lati- 

 tude. The greatest leaf area is exposed during May and June. 

 The small anemone-like flowers appear during April — June, each 

 lasting two or three days. The seeds mature in June and since 

 no seedlings have been found around the old plants in the 

 autumn, and seeds placed in the soil in the plant house did not 

 germinate until five months later, it seems safe to conclude 

 that their latent period ordinarily extends through the winter 

 following maturity. In the autumn the rhizomes send out 

 numerous runners which serve as a very effectual means of 

 propagation. The general aspect of the adult plant may be 

 seen in Plate 28 and Fig. 1. PL 29, and the seedling in Fig. 

 10 PL 29. 



