542 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tissue or clilorenchyme, and of the periderm, in the branches of plants 

 with few or no leaves. Such plants generally manifest a tendency to 

 preserve for a long time unchanged the cortex and the epiderm, in order 

 to render possible a sufficient assimilation ; the increase in thickness is 

 at first inconsiderable ; and hence the formation of periderm is retarded. 

 In some cases the periderm covers only a part of the branch ; in others 

 it grows in the form of spots or longitudinal lines scattered irregularly 

 over the surface, which, after a certain time, unite to form a continuous 

 periderm round the whole of the branch. When increase in thickness 

 commences, the necessary space for the new tissues is obtained by the 

 rounding of the branches which were at first flattened, or by the 

 enlargement of sinuosities, so that the assimilating tissue may be pre- 

 served for the longest possible time. In other cases the periderm is 

 developed a,mong the groups of assimilating tissue in the form of regular 

 longitudinal strips, which broaden in proportion to the increase in 

 thickness of the branch. This assimilating tissue may or may not 

 undergo subsequent changes. In Genista, where the groups of stereids 

 extend almost without interruption from the epiderm to the ieptome, 

 through the whole breadth of the outer cortex, the periderm is formed 

 in the middle of the strips of assimilating tissue, that is to say, at the 

 bottom of the original sinuosities, preserving for a long time at its two 

 sides remains of the chlorenchyme. 



Closing of the Bordered Pits in Coniferse.* — Herr K. Pappenheim 

 proposes for solution the question whether the bordered pits in the 

 alburnum of the wood of Coniferae are capable of being closed, and if 

 so, by what forces this is brought about. Taking the silver fi.r as an 

 example, he describes a mechanical apparatus by means of which he 

 claims to have proved that this can take place in the alburnum of the 

 spring and summer ; and he believes this fact to be of importance in 

 constructing a theoretical explanation of the course of the ascent of sap. 



Structure of Lecythidacese.f — M. M. 0. Lignier finds in the course 

 and arrangement of the vascular bundles a constant difference between 

 the Lecythidaceae (Lecythidese, Barringtoniefe, and Napoleoneae), and 

 the typical Myrtaceas. In the former the anterior and posterior bundles 

 of the leaf-stalk are branches from the margins of the main cauline 

 bundles ; the cortical bundles of the stem are normal leaf -trace-bundles. 



(4") Structure of Organs. 



Anatomy and Chemistry of Petals.t — Dr. E. Dennert describes the 

 structure and the colour of petals in a large number of plants. The 

 following are the more general results arrived at. 



As compared with foliage-leaves, petals show usually much less 

 development of tissue, and the veins are of simpler structure and less 

 branched. The number of stomates is usually comparatively small ; in 

 some instances, as the perianth-leaves of Ornithogalum umhellatum, they 

 occur on both sides ; in this plant long crystal-cells filled with raphides 

 occur between the epidermal cells. The cells of the epiderm of petals 

 do not generally exhibit any differentiation in the development of their 



* Ber. Deutsch. Bot. GeselL, vii. (1889) pp. 2-19 (1 pi.). 



t Ass. Frant;. pour I'Avancem. des sci., 1887, 9 pp. See Bot. Centralbl., xxxvii. 

 (1889) p. 145. 



% Bot. Centralbl., xxxviii. (1889) pp. 425-31, 465-71 513-8, 54.5-53. 



