l8 9i.] Anatomical and Physiological Researches. 309 



begins to develop. In the Cucurbitaceae, however, the differ- 

 entiation takes place at the same time, but even in this case 

 Lamounette will not allow the applicability of the term 

 "bicollateral." Every gradation in time of appearance is 

 found between the Cucurbitaceae and the Basellaceae in which 

 the appearance of the internal phloem is very late. 



Lamounette investigated the hypocotyl, stem and cotyle- 

 dons of a large number of plants by the aid of serial sections 

 cut by the collodion method. 



At the beginning of this year Leonhard published his re- 

 searches into the anatomy of the Apocynaceae 1 which show 

 that the internal phloem occurs throughout this order, with 



possibly one exception. 



In the August number of the Annals of Botany Scott and 

 Brebner have an extended account of their studies as to the 

 relation between the stem and root-structure in plants with 

 bicollateral bundles and the special modifications of the stem- 

 structure in plants which belong to this category. They ad- 

 here to the term bicollateral as a matter of convenience 

 without expressing any opinion as to the order of devel- 

 opment, and cite the term "vascular bundle," as a conven- 

 ient expression not now generally representing a well-de- 

 fined unit, but applied to vascular tissues even when the 

 limits of the individual bundles cannot be traced. "So long 

 as an internal phloem strand has the same longitudinal course 

 as the neighboring- bundles of the leaf-trace there is no serious 



b" uvllll b 



objection to regarding them as parts of the same formation." 

 "Bicollaterality is a character widely prevalent among the 

 most highly organized dicotyledonous families [18 are known] 

 and of great systematic value. It may fairly be maintained 

 that these orders represent in certain directions the most ad- 

 vanced types of dicotyledonous structure. 



44 The physiological importance of bicollaterality cannot be 

 fully estimated until the general question of the functions of 

 the phloem has been finally determined, but it is undoubtedly 

 great. The sheltering of a portion, often the larger portion, 

 of the delicate phloem within the woody cylinder is an obvi- 

 ous advantage, as is also the fuller utilization of the pith-area 

 and the consequent concentration of the tissues generally. It 

 is probable also that the pith-cells themselves may be able to 

 discharge both storing and conducting functions more effi- 



1 Botanisches Centralblatt, xlv. p. I. 



