248 SUMMARY OF CURRENT RESEARCHES RELATING TO 



stomata were hero found on the cotyledons ; but, on the other hand, there 

 were on the plunmlo and first leaves of the erect shoot. The same is 

 the caso with the Phaseoloidc;e. 



In other families of Dicotyledons the mother-cells of the stomata 

 were found on the cotyledons while still within the seed, substantially as 

 in CruciferoB and Compositae. The occurrence of the triangular mother- 

 cell is much less common among Monocotyledons. Those of grasses 

 are characterized by their oval form, and having almost invariably two 

 cells, one on each side, which distinguish them from all the other cells 

 of the epidermis. 



As the young stoma does not, in ordinary cases, reach quite as far as 

 the subjacent palisade-parenchyma, we have, in the air-space thus formed, 

 the first indication of the " breathing-hole." Very early the nucleus 

 loses its central position in the mother-cell of the stoma, and occupies a 

 somewhat higher position ; the protoplasm becomes turbid, and a few 

 pale-green chlorophyll-grains make their appearance. 



The processes are somewhat different in those cases, which occur 

 chiefly in evergreen and other coriaceous leaves, where the stoma is 

 depressed to a lower level than that of the other epidermal cells. In 

 the case of Allium Cepa this occurs not by any change in position of the 

 mother-cell of the stoma, but by energetic growth of the neighbouring 

 epidermal cells. In grasses, on the other hand, the mother-cell itself 

 tabes part in the difference of level ; and in Coniferas appears to be the 

 chief agent in the depression. In order to accomplish this the mother- 

 cell, as it developes, loses its oval form, and becomes wedge-shaped below, 

 the wedge forcing its way deeper and deeper between the epidermal cells, 

 which it forces aside, until it becomes so greatly depressed that it is 

 almost in contact with the palisade-cells. The fissure is not formed 

 until after this process is completed. 



Protecting-wood and Duramen.* — By " protecting-wood " (Schutz- 

 holz) Herr E. Prael understands that new wood formed on wounds, 

 which can be distinguished even by the naked eye from its brown 

 colour. The wood thus formed exhibits great resemblance to ordinary 

 duramen in the special cell-contents which characterize it — gum and 

 resin, and also in the occurrence of thyllae. The formation of thyllae 

 and of gum occurs in the same plant. The colouring of the cell-walls 

 is exhibited both by the protecting-wood and by duramen ; the identity 

 of the two is especially seen in coloured woods. The hermetical 

 closing of surfaces of the wood prevents, or at least hinders, the forma- 

 tion of protecting-wood. 



Split Xylem in Clematis.f — Dr. F. Krasser describes the peculiar 

 fissured appearance of the xylem in the vascular bundles of Clematis 

 Vitalba, which resembles that in the climbing Bignoniaceae, but results 

 from a different cause. It depends on the intermediate bundles between 

 the primary bundles originating later, and producing less xylem than a 

 leaf-trace bundle ; the difference in the radial development of the xylem 

 producing to the eye the appearance of a fissure. 



Apical meristem of the roots of Pontederiacese.J — Herr S. Schon- 

 land has examined the structure of the apical meristem in the roots of 



* Eer. Deutscli. Bot. Gesell., v. (1887) pp. 417-22. 



t Verhandl. K. K. Zool.-Bot. Gesell. Wien, xxxvii. (1887) pp. 795-8 (3 figs.). 



X Anu. of Bot., i. (1S87) pp. 179-82 (2 figs.). 



