88 MINXESOTA BOTANICAL STUDIES. 



nent characters. Sections were also, in many cases, cut from 

 material two years old for purposes of comparison. 



Since the structure of the hypocotj^l is often materially differ- 

 ent in all the three mentioned stages, it has seemed important to 

 make a record of the changes which take place during the first 

 year's growth. Previous investigators have not done this. 



A number of investigators who have made a comparative study 

 of root and shoot have incidentally examined the hypocotyl, 

 ^.^., Goldsmith [1876] and Gerard [1880 and 1881]. The 

 latter made some careful observations on the course of vascular 

 bundles from the cotyledons to the root. His statement that the 

 characteristic root structure often extends as high as the coty- 

 ledons is not, in general, confirmed by the present investigation. 



The most important articles* which need to be mentioned at 

 the present time are by Dangeard [1888 and 1889], Van Tieg- 

 hem [1891], and Flot [1889 and 1890]. Dangeard begins with 

 a study of the structure of roots, of which he distinguishes three 

 types. In the first type the root is diarch ; the hypocotyl has 

 four bundles in two pairs which arise as cotyledonary trace bun- 

 dles by the division of the midrib of each cotyledon. In the 

 second type the root is tetrarch ; the hypocotyl has eight bun- 

 dles in four groups. In the third type the root is octarch, while 

 the hypocotyl has sixteen bundles in eight groups. The first 

 type of structure of the hypocotyl above mentioned is the one 

 commonly found in the plants studied by the present writer who 

 has called it the " typical structure." (See General Conclu- 

 sions at the close of this paper.) 



Flot [1889, 1890] describes the " region tigellaire," a much 

 thickened portion of the axis of certain year-old seedlings. The 

 region extends from the base of the hypocotyl up to the first 

 foliage leaf or to some point between that and the cotyledons. 

 It is noted only in certain species. It is not the same as the 

 " tigelle," which extends only as high as the cotyledons. The 

 "region tigellaire" is characterized by only a slight develop- 

 ment of sclerenchyma and of normal phloem, while internal 

 phloem is probably altogether absent. The pericycle, he says, 

 is well developed. 



Van Tieghem [1891] divides the hypocotyl into "tigelle" 

 and " rhizelle." The growth of the hypocotyl is produced by 

 the elongation of either the tigelle, as in Rictmis, Acer, Cucur- 



* Search has been made, but without success, for a paper by Monal : Rech. 

 sur I'anat. compar. de la tige hjpocot. et epicot. 



