ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
477 
Cystolitks the author regards as reserve-structures for calcium 
carbonate, which may again serve for the transport of carbohydrates. 
Silica he finds, in opposition to earlier observations, to be excreted in 
young parts of plants in process of formation, as well as in the mature 
organs. 
A detailed description is given of the structures known as “ cover- 
cells ” (Deckzellen) or “ stegmata,” which occur in the interior of the 
tissue in certain groups of plants, viz. in the Palmae, the Scitaminese 
(except Zingiberacese), and some families of Orchidese ; in the Pandanaceae 
they are replaced by crystals of calcium oxalate. They are cells which 
contain within them a free mass of silica of varying form, and are always 
more or less in connection with the intercellular system. The author 
believes that they play an important part in promoting a current of air 
through the tissues, and also serve as temporary reservoirs for water. 
The main function of silica in plants is, however, one of mechanical 
strengthening. 
C3) Structure of Tissues. 
Morphology and Anatomy of the Axis.* — M. P. A. Dangeard adopts 
Gaudichaud’s terminology of “ phyton ” for the leaf, which constitutes a 
distinct individual, and consists of two parts — a cauline portion or rachis 
and an appendicular portion. The root is an ordinary axis which has 
undergone metamorphosis by the loss of its leaves, and the centripetal 
development of its protoxylem, which shows a close analogy with the 
central cylinder of Vascular Cryptogams. These phenomena are then 
studied in detail in two special genera. 
In Pinguicula there is, in all the species examined, a strongly dif- 
ferentiated endoderm in the stem ; it frequently displays thickenings on 
its lateral wall, and sometimes punctations on its other walls ; the cells 
of this layer often contain a violet sap. Where the foliar vascular 
bundle enters the stem it divides into two halves, each of which becomes 
a sympode, right and left ; these sympodes form a network, the size and 
form of the meshes of which vary according to the phyllotaxis. These 
sympodes may vary in two different ways. In the root of P. vulgaris 
the woody bundles may join in the centre or on the sides, and form a 
closed woody cylinder. 
In Acanthophyllum a woody genus of Caryophyllaceae, in which the 
leaves are more or less transformed into spines, the wood displays a great 
complexity of structure, recalling that of certain species of Bauhinia. In 
one section the leaf shows all transitions from the spiny to the ordinary 
form, in the diminution of the stereome, the reduction of the median 
bundle, the disappearance of the dorsal and increase in number of the 
lateral bundles, and the development of wings and of palisade-parenchyme. 
Comparative Structure of the Nodes and Internodes in the Stem 
of Dicotyledons.f — M. A. Prunet states that at the nodes the epidermal 
cells are frequently of larger dimensions, and an increase in the thickness 
of the cortical parenchyme may also be noticed, this being due rather to 
the enlargement of the cortical cells than to their multiplication in 
* Le Botaniste, i. (1889) pp. 175-207 (2 pis.), 
t Comptes Rendus, cx. (1890) pp. 592-5. 
