734 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Extra-floral Nectaries and Papillae in Diospyros.* — E. Elsler has 

 studied the extra-floral nectaries and papillae of the under side of the 

 leaf in Diospyros discolor, with the following results. The extra-floral 

 nectaries which attract the protecting ants are only functional for a short 

 time after the leaf -buds have opened. The nectaries attract the ants 

 owing to a peculiar sort of "eye-formation." Each "eye-nectary'' 

 consists of a glandular body formed of many small cells, sunk in the 

 mesophyll and separated from the latter by a layer of cork cells. These 

 cork cells appear before the nectary begins secretion, and prevent the 

 secretion from passing iuto the surrounding tissues instead of towards 

 the outside ; when the nectary has exhausted itself and drops off, the 

 cork closes the wound. At first the nectary is formed from a single 

 epidermal cell, but later on the subepidermal tissue shares in the forma- 

 tion of the nectary and the cork-layer. The papillae are formed on the 

 under side of the leaf by stiffened outgrowths from single epidermal cells. 

 The cuticle is very loose in the neighbourhood of the papillae, and forms 

 folds between the latter. It is probable that this arrangement is a pro- 

 tection against the leaf being used by animals as food. 



Extra-floral Nectaries of Melampyrum.t — H. Kirchmayr has studied 

 the extra-floral nectaries of M dampyrum, and finds that they are present 

 in M. arvense, M. nemorosum, M. barbatum, and M. pratense, but absent 

 in 31. silvaticum. They are not confined to the bracts, but are found on 

 foliage leaves and cotyledons ; in the latter case they function ashyda- 

 thodes. The stalk-cell of the nectaries is of great importance in the 

 regulation of pressure and in the exchange of material between the upper 

 glandular layer and the basal cell-layer. All the glands originally have 

 the same structure, but while the capitate glands retain their simple 

 structure, the shield-glands develop into hydathodes, and still further 

 modification results in the formation of nectaries. The latter serve to 

 attract the ants, which bring about seed-distribution, and possibly serve 

 to defend the plants against the attacks of snails. 



Leaf-fall and its accompanying Phenomena. J — E. Lowi has in- 

 vestigated leaf-fall in Ampelopsis hederacea, Ligustrum vulgare, Aitcuba 

 japonica, and other plants, and considers that there are six classes of 

 mechanisms bringing about this phenomenon :— (1) circular cell me- 

 chanism, (2) decomposition, (8) maceration, (4) turgescence, (5) change 

 in the cell-utricle, and (6) hard cell mechanism. Both the circular cell 

 and maceration mechanisms depend upon the combined action of tur- 

 gescence and decomposition of the cellular contents, but while in the 

 former the turgescence is the chief factor, in the latter decomposition is 

 most important. The .formation of separation -layers, which are found 

 in decomposition and changed utricle mechanisms, is due to modification 

 of the thickening of the cell-wall. In the decomposition mechanism the 

 cellulose breaks down until the cells are only surrounded by a thin mem- 

 brane corresponding to the innermost layer of the original wall. In 

 the cell-utricle mechanism the cell-membrane becomes thin through 



* SB. k. Akad. Wiss. Wien, cxvi. (1907) pp. 1563-90 (2 pis.). 

 t Op. cit., cxvii. (1908) pp. 439-52 (1 pi. and 1 fig.). 

 X Op. cit. cxvi. (1907) pp. 983-1024 (1 pi. and 14 figs.). 



