676 MINNESOTA BOTANICAL STUDIES. 



Russow, l3 in 1875, published an account of what was at that 

 time known concerning the vascular tissue of plants. In this 

 work the author discusses the evolution of the vascular bundle, 

 upward from the lowest type. In a classification of various 

 plants according to their bundles, he places the Onagraceae 

 among those in which there are two protophloem and oneproto- 

 xylem group in each vascular bundle. 



Bicollateral vascular bundles in the root of Onagra biennis 

 were discovered by Weiss 14 in 1880. Incidentally, this author 

 states that in the medullary phloem of the stem there are often 

 found thick walled bast cells and that these are not found in 

 the intra-xylar phloem of the roots. 



Peterson, 15 in discussing the bicollateral character of the 

 bundles in Onagraceae speaks of Oenothera odorata, and states 

 that the outer bast is but slightly developed while there is a 

 good development of inner bast which early forms an almost 

 continuous ring of tissue. Upon the border near the primary 

 bark is a nearly unbroken ring of bast fibres. Oe. gauroides 

 and Oe. longiflora are of like structure except that there are 

 also bast fibres in the inner phloem. According to Weiss the 

 same is the case with Oe. biennis (Onagra biennis). Most of 

 the Oenothera species have bundles of bast fibres in the outer 

 portion of the bast, and when cork formation takes place, which 

 occurs very often, the cork is developed internally to the fibres. 



Scott, 16 in an article in the Annals of Botany, devotes some 

 space to the consideration of internal phloem. This, he says, is 

 characteristic of a large number of dicotyledonous orders, usu- 

 ally, though not always very highly organized ones; Myrtaceae, 

 Onagraceae and all allied orders, Campanulaceae, Compositae, 

 Cucurbitaceae, etc. This internal phloem may occur as distinct 

 phloem strands or as a part of complete medullary bundles. 

 Internal phloem very often has cambial increase like the nor- 

 mal tissues. The article is followed by a good bibliography. 



Mile. Fremont 17 found sieve tubes in the pith of the root of 

 Oenothera f raseri and Oe. riparia. She also found them in the 

 secondary wood of the roots of Oe. parviilora, cruciata, macro- 



13 Russow. E . Betracbtungen iiber das Leitbiindel und Grundgewebe aus verglei- 



chend rnorphologischen und pbylogeaetischen Standpunkt. Dorpat. 1875. 



14 Weiss, J. E. Anatomie und Physiologie fleishig verdicktea Wurzeln. Flora. 63:97. 



1880. 



15 Peterson, O. G. loo. cit. 



16 Scott. On some recent Progress in our Knowledge of the Anatomy of Plants. An- 



nals of Botany . 4:147. 1889. 



17 Fremont, Sur les tubes crible's extraliberiens, dans la racine des Oenotherac^es. 



Morot. Journ. dc Bot. 5:194. 1891. 



