248 T. Holm — Anemonella thalictroides. 



of high palisades and three open strata of pneumatic tissue. 

 A few cells of collenclrymatic tissue support the leptoine side 

 of the larger veins, which are, furthermore, surrounded by 

 thin- walled parenchyma-sheaths. 



The development of collenchyina in Anemonella is rather 

 weak so far as concerns the stem and the leaves, and, as we 

 have seen from the preceding pages, stereome is the only 

 mechanical tissue that is represented in stem and petioles. A 

 very firm structure is, on the other hand, to be observed in the 

 achenium, when fully mature. We find here ridges of collen- 

 chyina and a ventral epidermis, of which the outer and radial 

 cell-walls are extremely thickened. There are eight collateral 

 mestome-strands, one in each rib, and they are surrounded, at 

 least partly, by thin-walled parenchyma sheaths. The chloren- 

 chyma represents a few strata of homogenous tissue with much 

 chlorophyll. 



In bringing together these facts derived from the internal 

 structure, our genus may be characterized as follows : The tu- 

 berous portion of the roots contains a broad secondary cortex 

 and pith ; the hadrome is represented by four short rays alter- 

 nating with four long ones, of which the latter are secondary ; 

 isolated strands of leptome occur in rays throughout the sec- 

 ondary cortex, but radiating from the center of the root and 

 located in the same radii as the eight rays of vessels. The 

 stem has no collenchyma, and no endodermis, but a closed 

 sheath of stereome, which surrounds the single circular band 

 of mestome-strands. The petiole shows the same structure as 

 the stem. The leaves are bifacial ; they possess normal pali- 

 sade cells, and the larger veins are supported by collenchyma, 

 besides that they are surrounded by typical parenchyma- 

 sheaths ; no stereome is developed in the leaves ; finally may 

 be mentioned that the stomata lack subsidiary cells. Anemo- 

 nella has, thus, a monostelic axis, while Thalictrum has an 

 astelic. However, the general structure of the North Ameri- 

 can Hanunculacew is so little known, that it is Impossible at 

 present to decide whether our genus, from an anatomical view- 

 point, is more closely related to Anemone than to some of the 

 other genera, even if the ovule possesses two very distinct in- 

 teguments, a character which it shares with Thalictrum. 



Brookland, D.C., April, 1907. 



EXPLANATION OF FIGURES. 

 Figs. 1 and 2. — Rhizomes of Anemonella thalictroides ; R = young roots, 

 which will become tuberous during the fall ; r = an old tuberous root from 

 the preceding year ; St.= base of flowering stern ; L = petiole of leaf ; nat- 

 ural size. Fig. 3.— Achenium. Fig. 4. — Same in cross-section ; both mag- 

 nified. Fig. 5. — Transverse section of pai't of tuberous root ; H = primor- 

 dial hadrome-ray ; H- = secondary hadrome-ray : L= secondary leptome; 

 x320. 



