136 T. Holm — Tsopyrum biternatum. 



and studied from a very few species. Marie* has presented 

 some notes on /. thdlictroides dealing with the vegetative 

 organs, and MacDongal (1. c) has studied the physiology of the 

 root tubers in our American I. biternatum. As a small con- 

 tribution to the knowledge of the internal structure of I. 

 bitematwm the writer has thought, that the following treatise 

 might be of some interest and assistance to future investiga- 

 tion of the genus. We do not believe, however, that this 

 anatomical characterization of an JEnemion would prove suffi- 

 cient for maintaining the genus of Rafinesque, but we wish to 

 demonstrate that some distinction exists, which may possibly 

 be strengthened further, when some investigator succeeds in 

 obtaining serviceable material of the other species. In Isopy- 

 rum biternatum the structure of the vegetative organs is as 

 follows : 



The roots. 



As it has been mentioned above, the secondary roots are 

 either slender in their entire length or moniliform; in the 

 latter the swellings occur in various places without any regu- 

 larity. The primitive structure may be observed in the capil- 

 lary, lateral roots, in which no increase in thickness takes place. 

 These roots are very hairy, and possess a distinct, thin walled 

 exodermis ; the cortex consists only of two strata ; a thin- 

 walled endodermis and pericambium surround two rays of 

 vessels, which extend to the center of the stele, alternating 

 with two strands of leptome. In the very long and slender 

 secondary roots, we find the same tissues, and of the same 

 weak structure, but the primary cortex is a little broader, con- 

 sisting of about four layers. Secondary formations have com- 

 menced resulting in the development of a broad secondary 

 cortex (Co in fig. 1), and in the development of secondary ves- 

 sels on the inner face of the primary leptome. Otherwise the 

 structure of the stele corresponds with that of the lateral roots, 

 there being only two rays of primary hadrome, which do not, 

 however, extend to the center since this is occupied by a small 

 cylinder of thinwalled, conjunctive tissue. This same struc- 

 ture occurs, furthermore, in the slender portions of the moni- 

 liform roots, and our figure 2 shows the peripheral tissues from 

 epidermis to the secondary cortex incl. In the swollen por- 

 tions of these same roots, the structure is of course somewhat 

 modified, but the modification depends merely upon a more 

 advanced increase in width of the secondary cortex. All the 

 other tissues are unchanged, and even the stele shows yet, and 

 very plainly so, the primitive diarch structure with two addi- 



*Eecherehes sur la structure des Benonculacees (Ann. d. sc, ser. 6, vol. 

 xx, Paris, 1885, p. 105). 



