ZOOLOGY ANJD BOTANY, MICROSCOPY, ETC. 93 



examined the structure of tlie sieve-tubes, and the development of the 

 secondary cortex in dicotyledons and gymnosperms. 



In Pinus sylvestris the sieve-tubes are nearly square, or longer 

 tangentially, especially in the autumn wood ; their walls are thin and 

 stratified, the tangential ones smooth, the radial and terminal pro- 

 vided with sieve-plates. These are divided by irregular ridges into 

 several compartments, each of which is perforated by from three to 

 six pores. A mixture of chloriodide of zinc, iodine, and potassium 

 iodide colours the cell- wall blue, the callus-structure reddish-brown. 

 The contents of the sieve-tubes, while in a functional condition, 

 consist of a parietal layer of protoplasm, mucilage, a watery fluid, 

 and starch-grains. At an early stage they contain several nuclei. 

 Later they lose their contents, and the sieve-tubes are either resorbed, 

 or remain more or less changed. 



The sieve-tubes of dicotyledons may be divided into two classes : 

 those which have sieve-plates on their more or less oblique terminal 

 walls only, and those which have them also on their lateral walls. 

 Those of monocotyledons agree with those of dicotyledons in essential 

 points ; they belong entirely to the second of these classes. They 

 contain less mucilage, and usually no starch-grains. Those of 

 Pteridophyta bear a close resemblance to those of monocotyledons, 

 especially in the EquisetacesB. In both cases they contain small 

 shining spherical bodies which are coloured yellow by iodine. 



Anatomy of Bark.* — J. Moeller publishes the results of a very 

 large number of observations on the structure of the bark of various 

 trees. As a general result he thus describes the three parts into 

 which bark may be divided : — 



1. The outer bark. The formation of cork may take place either 

 immediately beneath the epidermis, or in the epidermis itself, or it is 

 a second or deeper layer of the primary cortex ; the inner or outer 

 wall of the cork-cells may be sclerenchymatously thickened; the 

 periderm may be formed at an earlier or a later period ; it may be 

 sclerenchymatous or not ; the superficial periderm is sometimes 

 permanent. 



2. The middle bark. There may or may not be a coUenchy- 

 matous hypoderm ; the primary bundles may or may not contain 

 bast-fibres and sclerenchymatous cells ; crystals, single or in clusters, 

 frequently occur in it, or there may be glands. 



3. The inner bark. Bast-fibres and sclerenchymatous cells may 

 both be either present or absent ; there may or may not be crystals ; 

 sieve-tubes are a frequent constituent of it. 



Absorption through the Epidermis of Aerial Organs, j — M. Mer 

 states that in experiments on modes of destruction of the phylloxera, 

 it was noticed that when the woodwork in a vinery was washed with 

 coal-tar oil, the grapes acquired a strong flavour of coal-tar, while 

 the vegetative organs suffered scarcely any injury. It was remarked 

 that while the skin of the grapes remained nearly tasteless, the 



* Moeller, J., ' Anatomie der Baumrinden,' 447 pp. (146 figs.). Berlin, 1882. 

 t Comptes Rendus, xcv. (1882) pp. 511-4. 



