246 SUMMARY OF CURRENT RESEARCHES RELATING TO 



are distinguished from those of other species of Begonia by almost 

 invariably containing a mechanical element in the form of one or more 

 rows of sclerotized bast-cells running through their whole length. A 

 few of the weakest of the hairs are destitute of this mechanical element. 

 They are true emergences, being of hypodermal origin, and always 

 springing from a single meristem- or periblem-cell. The peculiarity of 

 these structures lies in their being emergences in which the sclerotized 

 element is not the epiderm but an internal skeleton. 



The leaves of the same species of Begonia contain also mechanical 

 elements imbedded in the assimilating-tissue in the form of sclerotized 

 branched bast-cells, resembling those of other thick-leaved plants such 

 as Camellia and Olea. Similar stereides also accompany the vascular 

 bundles of the veins and leaf-stalk. 



The author believes these peculiarities of structure to be connected 

 with the habit of the species, which is probably a native of dry sunny 

 localities. 



Scars on the Stem of Dammara robusta.*— Mr. S. G. Shattock 

 states that in Dammara robusta C. Moore, the base of the branch presents 

 a marked enlargement due almost solely to an increase of the cortical 

 parenchyme ; this excess serves to aid the wood in this situation 

 in supporting the branch ; the cortical parenchyme generally and the 

 medulla as well contain a considerable proportion of branching scler- 

 enchymatous idioblasts. In Dammara robusta the process of disarticula- 

 tion is like that by which a leaf or other organ is shed ; that is, the 

 parenchymatous cells across the whole zone of articulation multiply by 

 transverse division, a layer of cork resulting from the formation of this 

 secondary meristem, and through the distal limits of this the solution 

 of continuity occurs. It thus happens that the whole of the paren- 

 chymatous system of the stem is closed by cork before the branch is 

 actually shed. The branch-scar, when examined immediately after 

 disarticulation, is ovoid, concave, and has a finely granular surface; 

 the narrow circular zone of the fractured wood projects slightly at 

 the bottom of the cicatrical fossa, and in the cortical parenchyme are 

 imbedded the ruptured ends of the bast-fibres. 



Root-tubercles of Leguminosse.t — Dr. A. Prazmowski reviews the 

 various theories with regard to the nature of these structures and of 

 the organisms contained in them, and appends the results of observa- 

 tions and experiments of his own. 



In order to test whether the tubercles are normal or pathological 

 productions, he grew plants of Pisum sativum and Phaseolus vulgaris 

 in sterilized soil watered with distilled water and protected from all 

 possible access of microbes, side by side with others grown in normal 

 conditions or in sterilized soil and watered with ordinary water in 

 which soil had been soaked. In all of a large number of experiments 

 abundance of tubercles were found on the root in the latter cases, 

 while not a single one could be seen on those from which the possi- 

 bility of infection had been excluded. Under normal conditions the 

 tubercles appear to be formed about the time of the appearance of the 

 root-hairs. 



* Journ. Linn. Soc. Lond., xxiv. (1888) pp. 441-50 (1 pi.). 



t Bot. Centralbl., xxxvi. (1888) pp. 215-9, 248-55, 280-5. Cf. this Journal, 

 1888, p. 608. 



