NOTES ON RECENT RESEARCH. 



1131 



Belfast, 1902. — This note is of interest in the presence of older views, 

 and in the relations shown to exist hetween Dicotyledons and Monocoty- 

 ledons, usually regarded as fundamentally different. The author writes : 

 " The object of the present thesis is to show, from anatomical data, that 

 no hard-and-fast line exists between the two classes of Dicotyledons and 

 Monocotyledons. The hollow vascular cylinder of the stem of a great 

 number of dicotyledonous orders, if not of all, has been derived from a 

 system of scattered bundles, such as is characteristic of the stem of 

 almost all Monocotyledons. The flowering- stem and peduncle, as being 

 those parts of the caulome which have undergone least modification 

 owing to the necessities of adaptation to external conditions, exhibit, as 

 a rule, most clearly the primitive structure which in the vegetative parts 

 has become obscured. The axial organs of the seedling, owing to their 

 limited diameter and the small number of leaf- traces concerned in the 

 building-up of the vascular system, cannot as a rule possibly exhibit the 

 primitive scattered arrangement of the bundles. As the stem increased 

 in height and became more woody, and the leaves smaller and more 

 numerous, the scattered arrangement of bundles in the stem . . . gradu- 

 ally became modified into that of a hollow cylinder, which was necessary 

 both to support the bending-strains from a tall stem, and to facilitate 

 the continuous centrifugal addition of new conducting-tissues by means 

 of a secondary meristem. As far as the investigation has gone, the 

 primitive scattered arrangement of bundles can be traced in the stem of 

 about thirty dicotyledonous orders, viz. . . . and no doubt many more 

 will reveal it." The author then gives a number of other characters 

 very frequently accompanying the above feature in dicotyledonous stems. 

 Among them he instances the rudimentary character of many bundles, 

 representing those members of the vanishing scattered system which are 

 not destined to form part of the functional cylinder, and also the trimerous 

 character of some or all of the floral whorls. He mentions that several 

 orders exhibit 5-merous single perianth whorls, which (Jelakovsky has 

 shown is derived from two trimerous whorls by conversion of the lowest 

 perianth-member into a bract. " In some Monocotyledons, the scattered 

 bundles have become very peripheral, and even reduced to a single series 

 or row of bundles. In some cases amongst Dicotyledons where the 

 scattered arrangement has vanished from the stem, it can still be found 

 in the less modified foliage-leaf, especially where the petiole is cylindric 

 in contour or possesses a considerable diameter." In view of the facts 

 given, the author cannot, he says, agree with those writers who maintain 

 that the vascular structure of the seedling stem of Dicotyledons generally 

 proves to be primitively tubular in character.— B. I. L. 



Stem Formation. 



Vascular Tissue of Plants, The Evolution of. By W. C. Wors- 

 dell (Bot. Gaz. xxxiv. p. 217, No. 3 ; with seven figures in text). — The 

 author regards the most primitive form of stem -structure to have been a 

 solid stele or protostele consisting of a central mass of wood or xylem, 

 surrounded by a zone of phloem. This is illustrated in the apparently 

 most primitive forms of Ferns. 



