678 MINNESOTA BOTANICAL STUDIES. 



fleshy roots of plants with bicollateral stem structure contains 

 strands of phloem produced internally by the cambium. This 

 was found in various Onagraceae, Gentianaceae and Solanaceae. 

 In Oenothera longiflora Jacq., he found centrifugally formed 

 intra -xylar phloem in the root. Of this tissue the larger part 

 was seen to be parenchyma containing small groups of sieve 

 tubes. 



Solereder 23 made extended observations of phloem islands 

 in a large number of plants belonging to various families; the 

 Onagraceae were, however, not investigated. The researches 

 of Herail 24 and Kolderup-Rosenvinge 25 have also added to our 

 knowledge of these structures in certain genera. 



The investigations of Messrs. Scott and Brebner, 26 at first on 

 Strychnos, and afterward on numerous other plants 27 are of in- 

 terest. The writers criticize the work of DeBary, and find his 

 statement that the intra-xylar phloem in Strychnos is devel- 

 oped centrifugally to be incorrect. They find that there are 

 masses of crushed tissue at the outside of the islands, that the 

 islands grow from an internal cambium and that this growth 

 gradually crushes the older effete cells, farther out. In some 

 cases medullary rays may be seen extending through the 

 phloem islands. Thirteen plant families are enumerated in 

 which phloem islands occur. 



The subject has been investigated by Scott, 2S ' 29 Fremont, 30 

 Van Tieghem, 31 Leonhard 32 and others. A good drawing of an 

 island is given in Taf. 11, Jig. 8, in connection with Leonhard's 

 work, Chodat 33 - u has made a study of the different modes of 



23 Solereder. loc. cit. 



24 Herail. Recherches sur l'anatomie comparee de la tige des Dicotyledones. Ann. 



desSc. Nat. VII. 2: 1885. 



25 Kolderup-Rosenvinge. Anatoruisk Ondersogelse af Vegetationsorganerne hos 



Salvadora.— Oversigt K. Dansk. Selskabs. 1880-1881. 



26 Scott and Brebner. On the Anatomy and Hlstogeny of Strychnos.— Annals of 



Botany 3: 275. 1889. 



27 Scott and Brebner. On internal Phloem in the Root and Stem of Dicotyledons.— 



Annals of Botany 5 : 259. 1891. 



28 Scott. On some recent progress in our knowledge of the anatomy of plants.— An- 



nals of Botany 4: 147. 1889. 



29 Scott. On some Peculiarities in the Anatomy of Ipomoea versicolor Meissn.— An- 



nals of Botany 5 : 173. 1891. 



30 Fremont, loc. cit. 



31 Van Tieghein. Sur les tubes cribles extra-liberiens, etc. Morot. Journ. de bota- 



nique5:H7. 1891. 



32 Leonard. Beitnige zur Anatomie der Apocynaceen. Bot. Centtralbl. 45. 1891. 



33 Chodat, K. Contribution a l'etude des anomalies du bois. Atti del congresso bo- 



tanico internazionale di Genova. 144-156. 1893. 



34 Chodat, R. Nouvelles recherches sur l'origine des tubes cribles dans le bois. 



Archives des sciences physiques et naturelles, 1892. This and the foregoing 

 article are reviewed by Schimper in Bot. Centralbl. 55: 277. 1893. 



