ZOOLOGY AND BOTANY^ MICEOSCOPY, ETC. 89 



can always be induced by the production of tbese conditions ; as, for 

 example, in the Amygdaleee by tbe wounding of any part of the 

 stem, and the process of gummosis can then be followed step by step. 

 In the bird-cherry Prunus avium, this was found to be uniform at all 

 periods of the year, though the process was slower in the autumn. 

 The red colouring of the wood, which is always an indication of 

 gummosis, has its seat chiefly in the medullary rays. The brown 

 colour is due to the presence in the cells of gum in the form of small 

 granules, which are found especially on the cell-wall, or surrounding 

 the starch-grains, from which they partly result from metamorphosis, 

 partly also being a new formation. After four or five weeks, the cells 

 of the medullary rays are nearly filled with gum, and its formation 

 commences in the cavities of the vessels and wood-cells ; these also 

 now assuming a more or less yellow or red colour. This is frequently 

 accompanied by the formation of thyllee, which also help to fill up 

 the vessels. The purpose of this internal formation of gum, which is 

 analogous to the formation of resin in the Coniferse, is to form air- 

 tight plugs to the vessels. The dark colour of the duramen in many 

 trees is due to similar causes. 



A. Meyer * points out that a closing of open tracheids by plugs of a 

 peculiar substance takes place also in the fleshy rhizomes of some 

 monocotyledonous plants, e. g. Veiatrum album. He doubts, however, 

 whether, in either instance, this substance formed within the tissue is 

 properly described as gum. 



Oil-receptacles in the Fruit ofUmbelliferae.t — J. Lange describes 

 the development of these organs, both in general terms and in a 

 number of particular species. They originate from a group of four 

 similar cells distinguished from the others in the pericarp by their 

 greater refrangibility. They are arranged in corners of a square with 

 an intercellular space between them, which gradually developes into 

 the oil-receptacle. The secreting cells have very thin walls, and 

 clear translucent protoplasm ; the oil has a yellowish-grey colour. 



Influence of Cortical Pressure on the East-fibre.:j: — F. von 

 Hohnel calls attention to the displacement by which the bast-fibres 

 of Urticacese, many Asclepiadeae, Mimosese, and Linacese, when but 

 slightly or not at all lignitied, are broken up into a number of longer 

 or shorter segments, usually separated from one another by knots 

 composed of various simple or compound disks. This breaking up 

 results from the different segments of the same bast-fibre being 

 subjected to radial pressures of different intensities, by which they 

 are pushed apart. They consist either simply of sharp curvatures of 

 the fibres, or more often are connected with actual rupture of single 

 layers or of masses of layers. These knots were detected in about 

 two-thirds of between fifty and sixty species of dicotyledons examined, 

 but appear to be entirely wanting in monocotyledons. 



* Ber. Deutsch, Bot. Gesell., ii. (1884) pp. 375-6. 



t Lange, J., ' Ueber die Entwickelung der Oel-behalter in den Friicbten der 

 Umbelliferen,' 16 pp. (1 pi.) Konigsberg, 1884. 



^■Pringsbeim's Jabrb. Wiss. Bot., xv. (1884) pp. 311-26 (3 pis.). 



