ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 91 



forms, Dr, M. Mobius finds, in a number of species of Cactacese, 

 aggregations of the same substance closely resembling organic sphajro- 

 crystals. Their presence is of no value from a systematic point of 

 view ; since in the same genus there are species which contain, and 

 others which do not contain them. 



Anatomy of Combretacege.* — The order Combretaceae of Bentham 

 and Hooker consists of the two tribes Combreteae and Gyrocarpeae. 

 Herr H. Solereder, as the result of an examination of a large number 

 of species, considers that these groups have but little relationship to 

 one another. The Combreteae are characterized, with a few ex- 

 ceptions, by the presence of intraxylary soft-bast (within the xylem 

 on the medullary sheath), provided with sieve-tubes. The Gyro- 

 carpeas, on the contrary, have no bicollateral bundles, and a further 

 distinction from the Combreteae is furnished by the presence of 

 secreting cells, in the pith, the primary and secondary cortex, and the 

 leaves. This tribe may be again divided into two natural groups, 

 the Gyrocarpeae in the narrower sense (Gyrocarpus and Sparattanthelium) 

 and the Illigereas (Illigera), by the presence of eystoliths in the 

 former group, which are absent from the latter. 



Comparative Anatomy of the Stem and Rhizome in Herbaceous 

 Plants. t — Herr W. Eothert has made an extended examination of the 

 differences in anatomical structure between the aerial and underground 

 stems of herbaceous flowering plants. After a minute description of 

 the structure of the various elements in a great variety of plants, he 

 sums up the main points of difference under the following heads, viz. 

 (1) Differences regarding the relation of the central cylinder to 

 the cortex. In rhizomes the size of the central cylinder in com- 

 parison to that of the cortex is generally less than in underground 

 stems. (2) Differences relating to the mechanical properties of the 

 parts in question. These include differences in the position and 

 development of the sclerenchyma and collenchyma, air-passages and 

 intercellular cavities, and in the development of hairs, which are 

 usually, though not always, absent from roots. (3) Differences in 

 the development of suberous tissue, especially in the protecting 

 sheaths. These protecting sheaths are almost invariably present in 

 the rhizome, but absent from the aerial stem. (4) Differences in the 

 organized cell-contents. Chlorophyll is usually wanting in the 

 rhizome, with the exception of its apex in Mercurialis ; starch and 

 inulin are often more abundant in the rhizome. (5) Differences in 

 the differentiation of the tissues. This is generally less in rhizomes 

 than in underground stems. (6) Differences in the number, course, 

 arrangement, and structure of the desmom-tissue (vascular bundles). 

 The number of bundles is usually less in the rhizome than in the 

 aerial stem, and their arrangement less regular ; in Monocotyledons 

 the xylem and phloem have often a more or less concentric arrange- 



* Bot. Centralbl., xxiii. (1885) pp. 161-6. 



t Eothert, W., ' Vergleichend.-anat. Untera. iib. d. Dififerenzen in primaren 

 Bau der Steugel u. Rhizome krautiger Phanerogamen,' Dorpat, 1885. See Bot. 

 Centralbl., xxiii. (1885) p. 71. 



