ZOOLOGY AND BOTANY, MICEOSCOPY, ETO. 761 



connection could be traced between tlie formation of oil and tbat of 

 inulin. 



Besides tbe oil-passages, there occur in Inula Helenium, in tbe middle 

 of the root, special oil-receptacles bounded on all sides, also of schizo- 

 genous origin. In some roots (Inula Helenium, Cirsium oler-aceum, 

 G. canum, Tagefes patula, lappa tomentosa), a gradual separation takes 

 place sooner or later of tbe elements of the cortex, often aided by a 

 previous formation of cavities. In Inula and Lappa this proceeds so far 

 as to attack the oil-passages, and then the protecting-sheath, and even 

 parts which lie beneath it. 



Formation of Periderm.* — M. H. Douliot points out that, in con- 

 sidering the origin of the periderm, one has five cases to deal with, 

 viz. : — (1) Epidermal periderm ; (2) Esodermal periderm ; (3) Cortical 

 periderm ; (4) Endodermal periderm, and (5) Pericyclic periderm. In 

 the Eosacese, where the periderm is pericyclic, it is formed of layers of 

 hard cork, which from the first present on their radial walls foldings 

 analogous to those of the endoderm. The same phenomenon is shown in 

 the OEnothereee, and in several genera of Myrtaceae, where the periderm 

 is pericyclic. In the CEnotherese the periderm is in immediate contact 

 with the endoderm ; it is the same in the Eosacete. 



Protecting-wood and Duramen.! — Herr E. Prael, adopting Frank's 

 designation of " protecting-wood " (Schutzholz) for the brown-coloured 

 wood formed at spots where injury has been inflicted, has examined the 

 relationship in structure between this and ordinary duramen in a large 

 number of different trees. The following are the more important results. 



The protecting-wood formed as the result of injury always agrees in 

 structure with the duramen of the same species. The three substances 

 which fill up the vessels of the duramen — gum, resin, and thyllse — occur 

 also in the protecting-wood, in contradistinction to the alburnum of the 

 same age. The filling up by thyllje and by gum takes place in the 

 same plant ; larger vessels have a tendency to become filled by thyllse. 

 The colour of the cell-wall agrees in the alburnum and in the protecting- 

 wood. In some species the formation of thyllte in the wood takes place 

 at an early period ; the tendency to their formation is increased by age 

 and by injury to the wood. The strong colouring of the duramen is 

 produced by characteristic pigments, which are probably formed within 

 the cell, and infiltrate into the cell-walls when the tension of the cells 

 ceases. The intimate deposition of these in the cell-wall, and possibly 

 also a chemical combination with lignin, are the reason why they cannot 

 be entirely removed from the cell-wall by substances in which they are 

 soluble. Hermetic closing of cut surfaces of the wood prevents or 

 hinders the formation of protecting wood. The " wood-gum " of 

 Thomson must be regarded as a modification of cellulose. 



Causes which produce Eccentricity of the Pith in Pines.f — M. E. 



Mer states that transverse sections taken from the trunks of trees are 

 far from being always circular, especially towards the base. The pith 

 is often eccentric because the annual rings are not constant in thick- 

 ness. This is brought about by various causes, among which may be 

 mentioned : — The influence of the slope on which the tree grows, and 



• Morot's Journ. de Boi, ii. (1888) pp. 158-60. 



t Pringsheim's Jahrb. f. Wiss. Bot., six. (1888) pp. 1-81 (1 pi.). Cf. this 

 Journal, ante, p. 248. J Comptes Rendus, cvi. (1888) pp. 313-6. 



