02 SUMMARY OF CURRENT RESEARCHES RELATING TO 



produced by the unequal contraction of the non-lignified parts and 

 of the lignified thickenings. Tliis is very strikingly the case with 

 the spiral cells of the 'anther of Iris. The principle of dehiscence is 

 the s inie whether itj is longitudinal or by pores ; in the latter case 

 the fibrous layer has cither disappeared or is functiouless, except 

 towards the summit of each anther-lobe. The layer may be only one 

 cell or several cells in thickness, and presents various degrees of 

 complexity. Tlie dehiscence of the sporangia of some Heiiaticaa, 

 such as Cah/pogeia and Jungermannia, is brought about in precisely 

 the same way. 



Calcareous Glands of Plumbagineae.* — G. Volkens has examined 

 the calcareous incrustation which is frequently so conspicuous 

 on the surface of leaves of Plumbaginenc, in as many as seventy- 

 five species, and finds it to be due to the j^resence of calcareous 

 glands. These glands are globular, and are composed of eight cells 

 which proceed from a single epidermal cell. This divides first by 

 two septa vertical to the surface crossing one annther at right angles; 

 each of these four cells again dividing into two by a vertical wall. 

 All the walls cf these cells are remarkably thin ; they all contain a 

 dense finely granular protoplasm. These glands are secretion-organs, 

 developing and excreting in the first place a large amount of water, 

 which exudes as drops when evaporatiun is hindered. Their function 

 in the greater number of species belonging to the order is therefore 

 simply to counteract any abnormal relationship between the amount 

 of water given off by the leaves and the amount absorbed by the root, 

 and hence to serve as a jireveutative of excessive transpiration. But, 

 in addition to this, the glands serve, in a large ninnber of species, for 

 the elimination of superfluous salts of calcii;m, in the form of the acid 

 carbonate, which passes into the neutral salt on the evaporation of 

 the water. In some species this causes a calcareous deposit as thick 

 as tlie finger-nail. In order to prevent too great evaporation in 

 xerophilous species, these glands arc frequently dejjressed below the 

 level of tlic remaining epidermal cells. The calcareous incrustation 

 itself may also serve the same purpose. 



Protective Contrivances in the Bulbs of Oxalis.f— F. Hildebrand 

 describes the mode in which the bulbs of various American and 

 South African species of Oxalis are protected against the injurious 

 influences of the climate. In the former the bulbs consist of a large 

 number of scales, only the outermost of which, from their mem- 

 branous texture, are protective, the innermost serving only as reserves 

 of food-material ; while the intermediate scales, which form the bulk 

 of the bulb, serve both purposes ; these are often provided with silky 

 or glandular hairs. In the South African species, the bulb consists 

 of only a comparatively small number of scales, the innermost being 

 composed almost entirely of starchy parenchyma, and serving therefore 

 for nutrition, while the outer ones are protective only, and there is no 

 transition from one to the other. This is accompanied by a difference 



* Bcr. Dcutsch. Bot. Geeell., ii. (1884) pp. 334-42 (1 pi.), 

 t Ibid., pp. 108-11. 



