262 SUMMARY OF CUKRENT RESEARCHES RELATING TO 



are certain secreting canals which run from the median to the marginal 

 veins. The aquiferous system is closely related to these canals. It con- 

 sists of spiral tracheides, terminating obliquely or in a point, which are 

 grouped in a variable number of layers, embracing the lower and lateral 

 surfaces of the secreting canal. More rarely they are united into a bundle 

 lying completely below the canal, as in C. trapezifoUum and C. Thwaitesii, 

 or more rarely still, around the sides and upper surface, as in C. Pseudo- 

 tacamahaca. This apparatus is present in all the species. It communicates 

 with the bundles of the secondary veins by short fascicles of straight 

 tracheides, and fibres, which traverse the parenchyma. The endoderm of 

 the bundles is continued on the connecting fascicles and on the aquiferous 

 system. The author considers the apparatus may either be a hypertrophy 

 of the last ramifications of the fibrovascular system, the phloem of which 

 is extinct or represented sometimes only by some elongated parenchyma 

 cells, or it may consist of vascular reservoirs, due to the transformation of 

 parenchyma cells, despite the presence of endoderm. 



Vesicular Vessels of the Onion.* — In investigating the vesicular organs 

 with the object of determining whether or not the transverse walls are 

 perforated so as to place the cavities of successive segments in communica- 

 tion, Dr. S, H. Vines and Mr. A. B. Eendle have observed that, in the 

 quiescent winter condition of the bulb, there are patches of callus — easily 

 made conspicuous by staining with corallin — on the transverse walls. 

 From this they infer that the transverse walls are perforated, the canals 

 through them being open in the active, and closed by callus in the quiescent 

 condition of the bulb, just as is the case with sieve-tubes. This inference 

 has, however, to be confirmed by an investigation of the bulb in the active 

 condition. The authors also observe that each segment of a vesicular vessel 

 contains a large nucleus. 



(5) Structure of Organs. 



Origin of Lateral Roots.! — According to MM. P. Van Tieghem and 

 H. Douliot, while the terminal root is sometimes endogenous, as in grasses, 

 Canna, Tropseolum, &c., the lateral roots have almost always an endogenous 

 origin, the only exceptions being in the CruciferaB. The secondary roots 

 of all orders are always endogenous, while adventitious buds are usually 

 exogenous. With regard to the mode in which endogenous roots force 

 their way to the surface, the authors differ from previous observers. It is 

 not by compression and reduction, or any other purely mechanical mode, 

 but by the absorption or actual digestion of the contents of the cells of the 

 mother organ with which they come into contact. This purely physiological 

 process was observed by them in the case of terminal, lateral, and secondary 

 roots of a large nmnber of plants belonging to a great variety of natural 

 orders. If the cells attacked contain starch, this is first of all absorbed, 

 then the protoplasmic contents, and finally the cell- wall. 



The authors dissent from the conclusion of M. Mangin, J that the cortex 

 of the root originates, in Monocotyledons, from the central cylinder. As 

 the result of a large number of observations on plants belonging to 

 different orders of Monocotyledons, they assert that in all cases the central 

 cylinder of the root proceeds from the pericycle of the stem, while 

 the cortex and the root-cap have a common origin in the internal layer of 

 the cortex of the stem. 



* Proc. Cambridge Phil. Soc, Nov. 8, 188G. See Nature, xxxv. (1SS7) p. 214. 

 t Bull. Soe. Bot. France, viii. (188C) pp. 252-4, 342-3. 

 X See this Journal, 1SS3, p. 241. 



