64 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Primarily it comprises an investigation of the anomalies of the vascular 

 system in Campanulacese as far as concerns the aerial organs. In the 

 light of the general results obtained the author proceeds to a considera- 

 tion of anomalous vascular structure in Dicotyledons in general. The 

 following is a brief resume of his conclusions. In most cases abnormal 

 vascular tissues represent a part of the course of normal bundles. 

 Plants showing these anomalies form a series in which the normal 

 course of the bundles gets shorter and shorter, till finally it becomes 

 an abnormal bundle. The number of plants having such bundles is 

 very restricted. Leaf-trace bundles in their course through the stem 

 always diminish in volume from above downwards, whether they are 

 isolated or united sympodially. All, or nearly all the fibro-vascular 

 formations of the stem supply appendicular organs. "We must regard 

 these formations and part of those of the main root, as formed by the 

 bundles which descend from the foliar appendages of the stem (and 

 flowers). Rapidity of growth modifies this theoretical process of dif- 

 ferentiation, which does not affect older secondary formations. 



Development of the Central Cylinder of Aracese and Liliacese.* 

 M. A. Chrysler comes to the following conclusions from the study of a 

 number of examples from these two families. The members of both 

 families have primitively a collateral tubular central cylinder, or ecto- 

 phloic siphonostele, derived from a protostele and interrupted by gaps 

 above the points of exit of the foliar traces. Through these gaps the 

 external and internal phlceotermas communicate. The intrastelar paren- 

 chyma is to be regarded as having the same origin as the cortex, i.e. 

 both cortex and medulla are parts of the fundamental or ground tissue. 

 This primitive condition becomes altered : (1) by degeneration of either 

 the internal phlceoterma, or both internal and external phlceotermas ; 

 or (2) by the assumption of a medullary course by some vascular strands 

 with which leaf-traces are connected ; hence the scattered arrangement 

 of bundles is to be regarded as a cenogenetic character. The amphi- 

 vasal concentric strands are not a palingenetic feature, for they are 

 derived from collateral strands, and do not occur in the base of the 

 seedling nor in the leaves of floral axes. Anatomical evidence favours 

 the derivation of monocotyledons from dicotyledonous ancestors. 



Structure of the Sieve-Tubes of Angiosperms.t — A. W. Hill finds 

 that the sieve-plates on the end walls are pierced by relatively thick 

 slime strings, each of which is enclosed by callus. In the sieve areas 

 of the radial and tangential walls the slime strings are much smaller 

 than in the transverse sieve-plates, and three to six strings are enclosed 

 in one rod of callus. The author also finds numerous very short con- 

 necting threads between the sieve-tubes and the companion cells, which 

 during winter may be covered with callus on the side towards the sieve- 

 tube. Study of the development in the sieve areas shows that groups 

 of fine threads occur in the pit membranes in the lateral walls of the 

 youngest sieve-tubes. The threads are converted into slime, while the 

 surrounding cellulose membrane becomes changed into callus, thus 



* Bot. Gazette, xxxviii. (1904) pp. 161-84 (4 pie.). 



t Rep. Brit. Assoc. Meeting Soutbport, 1903(1904) p. 8. r >4. 



