76 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tissues of the cortex and bast form the greater part of this cushion. 

 At its base and in the neighbourhood of the bast of the stem is a hard, 

 horny tissue, consisting of extremely thick-walled cells, resembling 

 the bast-fibres, but short, also nearly iso-diametric, also of sclerenchy- 

 matous cells of great size, their cell-walls so greatly thickened that 

 the cavity has nearly disappeared, and with pit-canals. At a later 

 stage the woody tissue is also enclosed in the hypertrophy. Nothing 

 is said by the author about adventitious buds. 



Among parasitic fungi causing diseases of plants, Frank includes 

 species of Chytridiaceee, Saprolegniaceae, Peronosporeae, Ustilagine?e, 

 Uredineae, Hymenomycetes, Discomycetes, and Pyrenomycetes ; and 

 describes the following new species, viz. : — Saprolegnia Schachtii, on 

 Pellia ejnphylla ; Bamularia Vicice, on Vicia tenuifolia ; Cercospora 

 Phyteumatis, on Phyteunia spicatum ; and Gloeosporium Phegopteridis, 

 on Phegopteris polypodioides. The mycelium of Agaricus melleus he 

 regards as the cause of the extensive vine-disease known in France as 

 " blanc des racines." The sclerotial disease of rape-seed is caused by 

 Peziza sclerotioides ; and that of Impatiens glandulifera and other 

 species of Balsaminese by a fungus to which Frank gives the provi- 

 sional name Sclerotium Balsamince. The lowest internodes of the 

 stem lose their turgidifcy, become flaccid, and look as if they had been 

 boiled ; and the plant quickly dies. The tissue is penetrated by a 

 mycelium on which are small black sclerotia. 



A full account is given of the production of galls by Pliytoptus 

 and other gall-producing insects. The following description is given 

 of the formation of the bag-shaped galls on the leaves of Prunus 

 Padus. The insect probably in the first instance inflicts injuries 

 which excite the production of the galls ; but they only retreat into 

 the galls at a later period when the care for their offspring comes 

 into play. The same appears to be the case with Erineum tiliaceum. 

 The insect could not be detected either at the spot where the injury 

 is first made, or in the immature gall ; not till the beginning of 

 June, when they are found in abundance, with their eggs, in the galls. 

 In the case of the lime the injury appears to act on both sides of the 

 leaf. 



B. CRYPTOGAMIA. 



Cryptogamia Vascularia. 



Prothallium and Embryo of Azolla.* — Prof. S. Berggren has 

 followed out carefully the development of the prothallium and embryo 

 of Azolla caroUniana. 



As in Salvinia the endospore splits, on germination, along its 

 three edges. On escaping, the prothallium has the form of a slightly 

 convex disk, consisting in the middle of several layers of cells, at the 

 margin of only one, and separated below by a thin hyaline membrane 

 from the large protoplasmic spore-cavity. Shortly afterwards an arche- 

 gonium is formed near its centre, consisting of four cells enclosing the 

 oosphere and of four neck-cells. If this archegonium is fertilized, no 



* Lunds Univ. Arsskrift., xvi. ; aud Kev. Sci. Nat., i. (1881) pp. 21-31 (1 pL). 



