236 SCTMBIARY OF CURRENT RESEARCHES RELATING TO 



tractile organs appear to be specially characterized by the porous 

 nature of their comiionent tissues ; the more or less complete spongy 

 texture thus developed is fitted to allow of the ready distribution of 

 fluid contents. Where most developed, as in Mimosa pudica, there 

 are seen numerous finely jjorous cells, and masses which, in addition 

 to the fine jjores, have one or more large ostiola. Large intercellular 

 spaces are also well developed, and the vascular bundles are charac- 

 terized by an abundance of porous elements. Local differences in 

 the strength of the formed elements of the tissues, and the amount of 

 jirotoplasm and of chloroj)hyll corpuscles are also apparent. It is 

 pointed out that those areas in which diurnal functional activity and 

 the incident increased absorption and tension must attain a maximum, 

 are also those in which greatest facilities for the redistribution of 

 fluids are j^rovided by the nature of the structure. These must, 

 then, on the removal of the light, tend to arrive most rapidly at their 

 passive condition, and the changes consequent on this are probably 

 the cause of the early development of the " maximum nocturnal 

 position." 



Transparent Dots in Leaves.* — T. Bokorny has made a series of 

 observations on the transparent dots in leaves, in a large number of 

 natural orders, chiefly belonging to the Gymnospermas, Monocoty- 

 ledones, Apetalae, and Gamopetalse. The following are the more 

 imj)ortant general results: — 



In a great majority of cases the dots are organs of secretion, which 

 may be classified as follows : — 



1. Eesin- or Oil-glands, (a) Resin-cells cause transparent points 

 in the Laurineae, Monimiaceae, Piperaceae, a few Myrsinese, Meliaceae, 

 Sapindacege, Canellaceae, Anonaceae, and Magnoliaceae. (b) Resin- 

 cavities give this appearance in Salishuria, the Myoporineae, Myrsineae, 

 some Primulaceae, Samydeae, Myrtaceae, some Leguminos^, Rutaceas, 

 and Hypericineae. A clear distinction between these two is not 

 always so easy as might at first sight be supposed ; a close connection 

 may be established between resin-cells and lysigenous resin-cavities. 

 The latter merely represent groups of cells which secrete resin 

 internally ; the former similar solitary cells. In the former the 

 membranes of the secreting cells are finally absorbed, being only 

 rarely permanent, as in Myrospermum, while in solitary resin-cells the 

 persistence of the membrane is the rule, its absorption the exception. 

 Schizogenous resin-cavities differ somewhat more decidedly from 

 resin-glands. They resemble lysigenous resin-cavities in the grouping 

 of secreting cells, but differ both from them and from the unicellular 

 resin- glands in the secretion collecting outside the cells. In many 

 families, as for example the Laurineae, where there are internal glands, 

 external glands are wanting. 



The author considers the resins and volatile oils as true secre- 

 tions. In some cases, as in Laurineae and Piperaceae, it is certain 

 that the resin is made no further use of after its first excretion ; and 

 in no case was he able to detect any resorption of it. Volatile oils 



* Flora, Ixv. (1882) pp. 339-50, 355-68, 371-81, 387-97, 411-7. 



