ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
811 
lose, xylane, vasculose, and lignin, the mode of separating which is 
given in detail. The experiments were made chiefly on oat-straw ; but 
similar results were obtained from other parts of various plants — 
stems, leaves, fruits, &c. 
Conducting Tissues of Plants.* — Prof. E. Strasburger gives in this 
work a very full account of the structure, and of the adaptations to 
their purpose, of the tissues through which the currents of water pass 
in the living plant. 
Commencing with the Gymnosperms, he states that many of the 
Abietinese have medullary rays of complex structure, the wood-rays con- 
taining water-conducting tracheids as well as living parenchymatous 
cells, while most Conifers have bordered pits on the tangential surfaces 
of the latest formed autumn wood ; and the development of these 
two structures varies inversely. Both structures serve the purpose of 
providing a radial connection between the water-conducting tissues of 
successive annual rings. In both Gymnosperms and Dicotyledons there 
are always intercellular spaces containing air between the elements of 
the rays, and the living cells of the rays communicate by pits with 
these spaces. 
As regards the companion cells, their functions are fulfilled in the 
Abietineae by certain rows of cells belonging to the medullary rays of 
the phloem. In the other tribes of Coniferae the structure varies. The 
sieve-plates are never open so long as the sieve-tubes are functional. 
The callus is stated to be formed directly from the protoplasm, as it is 
also in Cucurbita. The arrangement of the sclerenchymatous elements 
of the bast in most Conifers is such as to preclude the possibility of a 
mechanical function. The vegetative structure of Gnetaceae more 
closely resembles that of Dicotyledons than that of Conifers. 
Passing on to Dicotyledons, the function of the living protoplasmic 
layer lining the walls of the sieve-tubes (in Cucurbita ) appears to con- 
sist in preventing diffusion from the tube, and in providing material 
for the formation of callus in order to close the plates when necessary. 
In Monocotyledons the thickening-ring differs from the true cam- 
bium of Dicotyledons or Gymnosperms in the fact that there is no 
single initial row of cells, to the divisions of which all the secondary 
tissues can be traced. The secondary tracheids are really such, and 
not true vessels. 
In Vascular Cryptogams, the author supports Van Tieghem’s view 
that the prevailing structure of the stem in Ferns is polystelic ; while 
the central cylinder of Lycopodium is regarded as gamostelic. 
In his summary of anatomical results, the author points out that 
the protoxylem of each new shoot is continuous, not with the pro- 
toxylem of the next older shoot, but with its later-formed xylem. In 
this way only can a continuous water-channel be maintained. He 
adopts the view that the water-current passes through the cavities of 
the tracheae ; and he describes a number of experiments carried out 
on different lines which appear to him to prove conclusively that the 
rise of water in the tissues of plants is a purely physical process, not 
* ‘ Ueber d. Ban u. d. Verrichtimgen d. Leitungsbahnen in d. Pflanzen ’ Jena 
1891 ; 1000 pp., 5 pis., and 17 figs. See Ann. of Bot., vi. (1892) p. 217. 
3 i 2 
