476 RECORD OF CURRENT RESEARCHES RELATING TO 



in most species of Finns, being in the form of a cylinder enclosing 

 the bundle. 



With respect to the structure of the tissue, the transfusion cells 

 have always, as described by Mohl, lost their primordial utricle, and 

 contain a clear sap, without any special secretion. Their function 

 is, in all probability, the conveyance of this sap, and not of air. 

 Although their appearance resembles that of ducts, they do not 

 contain true bordered pits ; and hence the appellation of trache'ides 

 sometimes given to them is unfortunate, since this term is con- 

 veniently confined to those vessels specially concerned in the convey- 

 ance of air. 



The true transfusion tissue should — according to Zimmermann, 

 who has recently re-examined its structure — be carefully distinguished 

 from the "transverse parenchyma " of Thomas, consisting of strongly 

 thickened bast-like cells with obliquely placed bordered pits, from 

 which it is always separated by a single layer of green parenchymatous 

 cells. 



Anatomy and Physiology of Fleshy Roots.* — Dr. J. E. Weiss 

 has investigated this subject in the case of a number of species 

 belonging to various families. The following are the general results 

 arrived at : — 



1. In all the roots examined the powerful development of xylem 

 is apparently intended to serve as a reservoir for reserve food- 

 material ; it is therefore thin-walled and ijarencliymatous, and takes 

 the largest share in the thickening. In rhizomes and tigella the 

 pith also serves the same purpose. 



2. In all plants which increase very rapidly in thickness and 

 which store up a great quantity of reserve food-material, a rapid 

 means of transport for these materials is essential. Since they are 

 not transported in the parenchyma by means of diffusion, but through 

 the sieve-tube by the open pores, the secondary phloem and fibro- 

 vascular bundles are of great importance in these plants. 



3. The secondary formations are more or less developed in 

 proportion to the longer or shorter length of life of the plant and to 

 the period at which lignification takes place. 



I. But the develoj^ment of these secondary formations depends 

 also on the thickness of the organ. 



6. As soon as the plant puts forth a stem above ground, the 

 secondary formations cease, and non-flexible elements take their 

 place. 



6. Secondary formations occur not only in those plants the 

 caulome of which has a so-called medullary phloem, but also in the 

 Cruciferee, where it is wanting, 



7. These secondary formations always decrease towards the apex 

 of the root, and are apparently directly connected with the primary 

 peripheral or medullary phloem. 



Csiuses of the Curvature of growing Organs, t — The curvatures 

 of the growing parts of plants have been attributed by physiologists to 



* ' Flora,' Ixiii. (ISSO)p. «1. 



t ' Ecv. Intcrnat. Sci.,' iii. (1880) p. 87. 



