T. Holm — I-sopyrum hiternatum. 139 



a ventral palisade tissue of a single layer, and a broader pneu- 

 matic tissue beneath this. The veins are surrounded by color- 

 less parenchyma sheaths, and the larger of these have a small 

 support of hypodermal collenchyma; the midrib differs from 

 the others by being embedded in a large, colorless water-storage- 

 tissue. If we compare now the structure of our American 

 species, I. hiternatum of the section Enemion, with the 

 European I. thalictroides, which is an Euisopyrum, we notice 

 the differences as follow. According to Marie (1. c.) the 

 roots of I. thalictroides are only slightly tuberous near the 

 base with small development of the secondary cortex. In 

 I. fumarioides of the section Leptopyrum, examined by the 

 same author, the primary root is developed as a tap-root, in 

 which the secondary leptome forms a continuous zone around 

 the broad cylinder of hadromatic rays with strata of paren- 

 chyma, while the secondary cortex represents a rather small 

 tissue. We have thus in Leptopyrum the common type of an 

 annual primary root, developed as a tap-root, while in Enemion 

 the primary root becomes replaced by secondary, which are 

 either slender, or moniliform (I. hiternatum), or simply 

 tuberous ( 1. stipitatum) ; in Euisopyrum, the secondary 

 roots are very long and only slightly tuberous near the base. 



In regard to the rhizomes of I. hiternatum and /. thalic- 

 troides the structure is identical. But the stem above ground 

 shows some points in which these species differ from each 

 other. M-arie (1. c.) observed in /. thalictroides an endodermis 

 and a pericycle of two zones, an outer very heavily sclerified, 

 and an inner more thinwalled. We remember that in /. hiter- 

 natum no endodermis was observed, and that the pericycle was 

 composed of only three layers of thinwalled stereome. But 

 otherwise the structure of the stele shows no difference of 

 importance. It is, thus, merely in regard to the relative 

 development of the .mechanical tissue in the pericycle that 

 these two species differ from each other, so far as concerns 

 the stem structure. While in /. thalictroides the structure 

 of the petiole is identical with that of the stem, we notice in 

 I. hiternatum that the petiole lacks the mechanical support of 

 stereome and collenchyma. In the leaf-blades of I. thalic- 

 troides Marie observed a large-celled epidermis with the outer 

 walls convex on the dorsal face, and an almost homogeneous 

 chlorenchyma, since the palisade tissue is barely differentiated ; 

 the leaf structure of this species is, thus, quite different, from 

 that of our I. hiternatum, as described above. 



The anatomical structure of these two species of Isopyrum, 

 representing Euisopyrum and Enemion, does not indicate that 

 these plants might belong to two distinct genera. The exter- 

 nal structure, however, is very different, if we consider the 



