182 SUMMARY OF CUERENT RESEARCHES RELATING TO 



Structure and Development. 

 Veg-etative. 



Asymmetry of Compound Leaves.* — Ph. van Tieghem has exa- 

 mined the lateral leaflets and the stipules of numerous types of compound 

 leaves, and is led ,to the following conclusions. Whatever may be the 

 number, form, size, and arrangement of such leaflets, they are asym- 

 metrical ; when stipules also occur, they share in this want of symmetry. 

 The asymmetry of the leaflets is so arranged as to preserve the bilateral 

 symmetry of the entire leaf. More frequently the lower portion of the 

 leaflet or stipule is the more highly developed, but the reverse may be 

 the case. Sometimes the upper portion of the leaflets is the greater, 

 while the stipules of the same leaf are larger towards the base, and vice 

 versa. Both kinds of asymmetry occur side by side in the same families. 

 Stipules, whether of a simple or of a compound leaf, are always asym- 

 metrical. 



Intracellular Formations in Rhamnus cathartica L.f — W. Ticho- 

 mirow has Investigated the intracellular formations of the leaf of 

 Rluimiius cathartica, and tiuds them precisely similar to those of the 

 fruit of tlie sanie plant. These formations are cylindrical, and are found 

 in the palisade layer, in the neighbourhood of the vascular bundles, and 

 in the spongy mesophyll. 



The author also finds that in the fruit, the intracellular formations, 

 which are colourless during life, become bright red when exposed to the 

 air, owing to the presence of an oxydase. 



Structural Account of Aptosimum Burch. and Peliostomum 



E. Mey.|— Emil Weljer describes the results of his investigations, partly 

 structural, partly systematic, on these two genera of South African 

 plants, members of the order Scrophulariacese. Aptosimum, the larger 

 of the two genera dealt with, now numbers twenty-eight species, all, 

 with one exception, natives of Africa south of the equator (Angola^ 

 German S.AV. Africa, Rhodesia, Transvaal, Orange River Colony, and 

 the Cape). None have yet been found in Natal. They are, therefore, 

 xerojihytes, and their structure clearly shows adaptation to xerophytic 

 conditions. Bentham's classification into two groups, spine-bearing and 

 unarmed, the author finds to stand the test of microscopic examination, 

 since only two of the nineteen species of the first group show anatomical 

 peculiarities markedly different from the rest. The epiderm (always of 

 one layer) of the leaf has a thick outer wall, in some cases strongly, in 

 others slightly cuticularised. The hypoderm above and under the mid- 

 rib extends up to the epiderm, its outermost cells being collenchymatous. 

 Trichomes afford help in the dissemination of species. The assimilation 

 tissue usually consists, on both sides of the leaf, of short palisade cells 

 with but few intercellular spaces. Stomata, rarely suuk below the sur- 

 face, are found in equal numbers on both sides. The structure of the 

 midrib is important in classification. In the sub-genus S2}inosa, the 



* Ann. Sci. Nat., iv. (1906) pp. 211-22. 



t Comptes Rendus, cxliii. (1906) pp. 922-4. 



X Beih. Bot. Centralbl., xxi. 2te Abt. (1906) pp. 1-101 (3 pis.). 



