ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 69 



the more rapidly growing secondary meristem for each developing leaf. 

 Since each leaf is supplied with strands from cauline bundles in different 

 parts of the stem, those strands which come to it from the opposite side 

 of the stem describe almost a semicircle to reach the leaf ; those which 

 arise on the same side of the leaf pass directly into it, and small arcs are 

 described by strands which arise in intermediate positions. There is no 

 extrafascicular cambium or any other vestige of polystely. A. B. R. 



Polyxylic Stem of Cycas.— W. L. Miller {Bot. Gaz., 1919, 68, 

 208-21, 11 figs.). The author has studied the cambium of the stem of 

 Cycas media in order to discover the origin and subsequent development, 

 and to form some definite conclusions concerning the unusual method 

 of secondary growth of the vascular elements. He has examined the 

 xylem and phloem of the normal and first cortical cylinders of the 

 full-grown stem, and finds that the vascular cylinders are of unequal 

 length. The normal cylinder begins to differentiate at the meristem, 

 while the others begin at successively lower joints ; thus the normal 

 cylinder is the only one which has its origin in the procambium, and 

 which forms protoxylem and protoplasm. The protoxylem is usually 

 scalariform, but elementary spiral tracheids are not infrequent. The 

 primary xylem is also scalariform, while the secondary xylem is pitted. 

 In the first cortical cylinder there is neither protoxylem nor protophloem ; 

 the xylem cells are mostly pitted, but a few scalariform tracheids are 

 present. In the secondary phloem of both cylinders suberised bast- 

 fibres are relatively numerous in comparison with the sieve-tubes. The 

 origin and development are similar in all cortical cylinders, and their 

 appearance is probably connected with the plant's periods of activity and 

 rest. No material was available for studying the differentiation of 

 cortical cambium. S. G. 



Companion-Cells in Bast of Gnetum and Angiosperms. — W. P. 

 Thompson {Bot. Gaz., 1919, 68, 451-9). In previous papers 

 the author has indicated the existence in Gnetum of elements in the 

 bast resembling the companion-cells of the angiosperms. The present 

 is a comparative study of their structure and development. Companion- 

 cells resembling those of angiosperms in size, in their association with 

 sieve-tubes, in their usual location in the angles of the sieve-tubes, and 

 in their vertical elongation, are present in the bast of some species of 

 Gnetum. The development of these companion-cells, however, is quite 

 different from that found in angiosperms. Whereas, in the latter, each 

 sieve-tube and its companion-cell are derived from two successive cells 

 in a single row of cambial products, in Gtietum sieve-tubes and companion- 

 cells are produced from different rows of cambial cells. Thus although 

 the completed forms of companion-cell in the two groups are similar, 

 they have probably been independently evolved. Primitive conditions 

 in which companion-cells are lacking, or in which continuous rows of 

 companion-cells are present, are found in certain regions of some species. 

 Thus they are absent in the young stem of G. moluccense, also in seed- 

 lings of several species and in reproductive axes. The parenchyma of 

 the wood is formed by those cambial cells which form companion-cells ; 



