502 MINNESOTA BOTANICAL STUDIES. 



My attention was first called to the somewhat peculiar feat- 

 ures of the anatomy of the tubers in 1888 and since that time I 

 have had the plant under more or less continual observation in 

 the botanical laboratories of De Pauw and Purdue Universities, 

 the State University of Minnesota, and the Botanic Institute, 

 Leipsic, as well as in the natural habitats of the plant, with 

 the result that some noteworthy features of the mechanisn of 

 protection and storage of reserve material have been brought 

 to light. 



Anatomy of roots and tubers. The long slender roots are 

 closely crowded together at the point of origin on the internodes 

 of the rhizome, and since they penetrate a loose friable moist 

 soil, are only slightly geotropic, and grow very slowly with but 

 little expenditure of outward work in the way of external pres- 

 sure. As a natural accompaniment of this method of growth, 

 only a rudimentary root cap has been developed and the zone 

 of root hairs extends to within 1 or 2 millimeters of the tip. 



In a discussion of the features of the morphology of the 

 roots of the Ranunculaceae, Mr. Maxwell (VIII) has without 

 examination classed the roots of Isopyrum among those of 

 tetrarchic formation. It is seen, however, to be diarchic (Fig. 

 2, PI. 29). The formation of the secondary hadrome and 

 differentiation of the endodermis only slightly precedes the 

 development of the root-hair cylinders of the piliferous layer. 

 It has been observed that in some instances the formation of 

 the tuber began simultaneously with, or immediately folio vving 

 the appearance of the secondary hadrome, and previous to the 

 formation of the root-hairs, although it does not usually begin 

 until some time later — a fact which accounts for great dif- 

 ferences in the cortex of the mature tuber. The secondary 

 hadrome is formed from the arches of meristematic tissue 

 lying between the two groups of primary vessels, and the 

 lateral vessels of the secondary hadrome border directly on 

 the innermost vessels of the primary hadrome, both in normally 

 thickened roots and in tubers, thus forming an irregular ring. 



The formation of a tuber consists primarily in the exaggera- 

 ted external development of the pericycle, which retains in 

 greater part its meristematic character even in old tubers, 

 coupled with a co-ordinate extension of the cambiform rays 

 (assise ge'neratice of Van Tieghem XIV) Fig. 4 PL 29 which en- 

 force tangential growth in the endodermis and cortex. The 

 mass of cells formed from the pericycle are entirely without 

 intercellular spaces. The nuclei of these cells lie in the lining 



