76 SUMMARY OF CURRENT RESEARCHES RELATING TO 



light, and the heart- wood of relatively small diameter ; in Biota the 

 wood is thicker and harder, and the heart-wood is of relatively large 

 diameter. The structure of the medullary rays is also distinctive ; in 

 similar sections of plants of equal age, the number of cells in Thuja is 

 as 2 : 3 or 2 : 3 • 5 ; the ratio between the breadth and the height of the 

 central cell is 1*29, or 1-3 in Tliuja and 1 : 1 * 5 in Biota. The pits on 

 the radial walls of the tracheids of Thuja are large and the surrounding 

 chamber relatively small, while the reverse is the case with Biota. The 

 intercellular spaces between the tracheids and medullary rays are three- 

 cornered in tangential sections of Thuja, while in Biota they are forked 

 and branch out into small canals, sometimes terminating in a star-shaped 

 space between the parenchyma-cells. 



Anatomy of Chlorophyll-tissues.* — S. Rywosch has studied the 

 anatomy of the leaves of various species of Conifers and Monocotyledons, 

 with special reference to the chlorophyll tissues. In Finns the meso- 

 phyll is undifferentiated, the palisade-cells being entirely absent, but 

 continuous lamellse pass from the upper to the lower surface of the 

 leaf and form a system of air-chambers. Certain Monocotyledons, e.g. 

 Iris gennanica, have the same type of leaf. In Abies and Cephalotaxus 

 the palisade- tissue is developed, but lamellas and corresponding air- 

 chambers are found in the under parts of the leaf ; the same type is 

 found in such Monocotyledons as Phormium tenaximii Veratrum album, 

 while Lilium Martagon agrees in some respects but shows more marked 

 dorsiventrality. The writer disagrees with Haberlandt in regarding 

 these variations as connected with assimilation, but believes them to 

 bave reference to the aeration of the leaf. The " Trichter " cells, which 

 Haberlandt likewise thinks to be connected with assimilation, appear 

 to hinder rather than assist the conduction of the products of assimila- 

 tion to the vascular bundles, and are regarded as having some connexion 

 with aeration. 



Finally, the author believes that the palisade-cells themselves owe 

 their form and position to the rapid evaporation of water, and supports 

 his views by reference to plants in dry regions which have a high 

 coefficient of evaporation consequent upon the dryness of the surround- 

 ing air, and floating plants which also give off large quantities of aqueous 

 vapour as a result of their great absorption of w^ater ; both classes of 

 plants have well-developed palisade-parenchyma, but with decreased 

 evaporation the palisade-cells likewise decrease in number and size, as 

 in those desert-plants which have succulent leaves. 



Secretory Organs of Ferula.f — 0. Tunmann has studied the 

 schizogenous lactiferous vessels in seedlings of Ferula Narthex. The 

 primary root is diarch or tetrarch and of normal structure, and until 

 after the seedling is nine months old, is scarcely distinguishable from 

 the rhizome. No anomalous structures are found until the plant is 

 more than two-and-a-half years old, but during the first year a ring of 

 cork is formed just below the cotyledonary node, which encloses all the 



* Zeitschr. Bot., iv. (1912) pp. 257-78 (7 figs.). 



t Ber. Deutsch. Bot. Gesell., xxx. (1912) pp. 245-57 (1 pi.). 



