172 SUMMARY OF CURRENT RESEARCHES RELATING TO 



minosaa, and attempts to found a system of classification on characters 

 described from this source. The paper is profusely illustrated with 

 plates of the anatomical details, and a very copious bibliography is 

 appended. 



Branching of the Vegetative Organs.* — M. Eaciborski treats this 

 subject under the following heads: — (1) The radial or dorsiventral 

 structure of the shoot; (2) the arrangement of the leaves, both in longi- 

 tudinal direction and in their lateral distance from one another (in- 

 cluding dimorphism or anisophylly ; (3) periodicity in the formation 

 of the twigs ; (4) lateral distance of the twigs from one another ; (5) the 

 specific length of the axis ; (6) the position of the branch which bears 

 the twigs ; (7) other influences. Of these, Nos. 3-5 are treated of in 

 detail in this paper, with a large number of illustrations from tropical 

 trees and shrubs. 



Causes of the Vernation of Leaves.f — W. Arnoldi classifies the 

 causes which determine the position of the leaves in the leaf-bud under 

 two heads — internal and external. The former are dependent on the 

 localisation of growth in the embryo ; the latter on the conditions of 

 space. The inner causes must be assumed ; we are unable to explain why 

 some few leaves display a long-continued apical growth, while in others 

 this ceases at an early period ; or why, in many leaves, there is always 

 an unequal growth of the two halves ; or why the under side of the leaf 

 grows more rapidly than the upper side, causing a circinate vernation. 

 By the removal of the stipules of Magnolia the leaves remain flat in the 

 bud ; the crumpled aestivation of the petals of Papaver may be pre- 

 vented by the removal of the calyx ; showing that the external causes 

 which determine the vernation are readily modified. 



Appendicular Organs of the Leaves of Myriophyllum.| — E. Perrot 

 calls attention to the presence in several species of Myriophyllum (yerti- 

 cillatum, spicatum, &c.) of peculiar minute lamellar appendages in the 

 axils of the segments of the leaves, at their apex, and distributed irregu- 

 larly over their surface. They are extremely caducous, leaving a smooth 

 scar. They are not, as has been stated, of a stipular nature, but are 

 entirely trichomic ; no useful function can be readily assigned to them. 



Glandular Hairs of Salvia glutinosa.§ — Prof. L. Macchiati states, 

 as a fact beyond question, that the glutinous hairs which cover the stalk 

 of the inflorescence of this plant secrete a peptonising ferment, through 

 the agency of which the insects captured by the secretion are digested, 

 as in the sundew or Venus's fly-trap. 



Roots of Cactacese.|| — In several species of Cactaceaa natives of 

 Arizona, C. E. Preston notes that there are two distinct root-systems, 

 a horizontal and a vertical, of which the latter are developed first, while 

 the former perform the chief part of the absorptive function. The 

 horizontal roots are always very brittle, the vertical ones being more 

 elastic. The woody cylinder in large absorptive roots is much smaller 



* Ann. Jard. Bot. Buitenzorg, xvii. (1900) pp. 1-67 (31 figs.). 



t Flora, lxxxvii. (1900) pp. 440-78 (46 figs.). 



X Journ. de Bot. (Morot), xiv\ (1900) pp. 198-202 (5 figs.). 



§ Bull. Soc. Bot. Ital., 1900, pp. 327-8. 



|| Bot. Gazette, xxx. (1900) pp. 348-51. 



