ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 551 



regarded as resulting from an arrest of development, frequently repro- 

 ducing the form which the whole plant originally possessed. In many 

 plants this youthful form disappears rapidly and at a very early period ; 

 while m others it remains for a very considerable time, according to the 

 external conditions of life. 



"Tan-disease" of Cherries.* — Dr. P. Sorauer describes a new 

 disease of cherries similar to the well-known " tan-disease " of apples, 

 which has made its appearance in Germany as the result of a wet 

 summer. It manifests itself in the excessive development of the lenticels 

 by the formation of fresh layers of cork beneath those previously in 

 existence, and by a subsequent copious formation of gum. The latter 

 appears to be the result of a great local accumulation of water and of 

 formative substances. 



Diseases of Trees.f — Dr. E. Hartig has published a second edition of 

 his ' Text-book of the Diseases of Trees,' including those due to all 

 causes : — external injury, unfavourable conditions of life, and the attacks 

 of parasites, whether j)hanerogamic or cryptogamic. Among destructive 

 fungi he describes in particular Melampsora Tremulse, which attacks 

 both the Scotch fir and the larch, Phoma ahieiina on the silver fir, 

 Triclwsjphseria parasitica and Herpotrichia nigra, which are very de- 

 structive to forest-trees, Pestalozzia Martigii, and many others. 



B. CRYPTOGAMIA. 



Cryptogamia Vascularia. 



Aluminium in Vascular Cryptogams. J — Prof. A. H. Church finds 

 aluminium to be a constant constituent of the ash of some species of 

 Lycopodium, while it is entirely absent from others. Among other 

 Vascular Cryptogams, the genera Equisetum, OpMoglossum, Salvinia, 

 Marsilea, Psilotum, and Selaginella gave negative results ; it was found 

 only in the ash of some tree-ferns, but is an important constituent of 

 the water-moss Fontinalis antipyretica. It occurs in combination with 

 organic acids, and may serve to neutralize the acids produced in the 

 plant. 



Germination of the Megaspore of Isoetes,§ — According to Mr. J. B. 

 Farmer, the coat of the megaspore of Isoetes lacustris consists of six 

 layers : — the ej)ispore, derived from the epiplasm of the megasporange, a 

 colourless, glassy, and brittle layer, whose surface is beset with numerous 

 irregular prominences ; the exospore, composed of three brown cuticu- 

 larized layers ; and the endospore, composed of two layers of cellulose. 

 The protoplasm of the megaspore is remarkably gi-anular, and contains 

 a large quantity of starch and oil, and a sharply differentiated nucleus. 

 The first indication of cell-division in the formation of the prothallium 

 is the appearance of a very thin membrane of cellulose derived directly 

 from the protoplasm, which cuts the spore into a basal and an apical 

 portion ; while the former for some time undergoes no change, the latter 



* Bot. Ztg., xlvii. (1889) pp. 181-6. 



t ' Lehrb. d. Baumkraakheiten,' 2 Aufl., 137 figs, and 1 coloured pi., Berlin, 1889. 

 See Bot. Ztg., xlvii. (1889) p. 272. 



X Proe. Roy. Soc. Loud., xHv. (1888) pp. 121-9. 



§ Op. dt., xlv. (1889) pp. 306-8, and Ann. of Bot., ill. (1889) pp. 131-4. 



