62 SUMMARY OF CURRENT RESEARCHES RELATING TO 



parenchyma of the medullary rays gives rise to supernumerary masses of 

 phloem in the secondary stem. No interfascicular cambium is present, 

 but there is much dilatation of all the parenchyma. 



Origin of Leaves and Stem.* — L. Flot has contributed the last of 

 his series of papers dealing with the origin of the leaves and stem. The 

 following are the conclusions formed by the author. The first differen- 

 tiation of the meristematic apex of Phanerogams consists in the forma- 

 tion of foliar outgrowths arising from a layer of cells which ultimately 

 gives rise to a vascular meristem. The latter forms cortex and epidermis 

 both above and below, and in the centre is differentiated into ordinary 

 fibro- vascular tissue. The direction of growth is determined by the 

 different pressures on the terminal bud, being greatest where the pressure 

 is least. The outgrowth thus formed constitutes a foliar segment and 

 ultimately develops into a typical leaf. The stem-structure is first 

 determined by the structure and anastomoses of the young leaf -bases, 

 and when these are complete, the whole mass of cortical and vascular 

 tissue and epidermis constitutes the stem. When once the stem has 

 thus been formed, the lower cells of each leaf-base rapidly multiply and 

 so form internodes, thus causing the stem to increase in length. 

 Increase in thickness may be brought about by increase in the number 

 of bundles, and this is in accordance with the number of leaves ; or it 

 may be due to the appearance of new meristematic layers, but even then 

 it is possible to discover the traces of the primitive leaf -structure. 



Water-stom^ta of the Lobeliacese.f — M. Tswett has made a careful 

 study of the hydathodes of Lobelia Dortmanna, Lobelia splendens, and 

 Lobelia fulgens. While confirming the descriptions of these structures 

 given by Buchenau and Minden, the author claims that the stomata 

 found in connection with them represent quite a new type. The 

 opening of each stoma is divided into halves by a thickened, cutinised 

 partition which stretches from one extremity of the guard-cells to the 

 other. In several cases this cutinous membrane is continued right over 

 the opening so as to completely close it. Twenty other species of 

 Lobeliaceas have also been examined, nineteen of which have similar 

 stomata, while the remaining one is doubtful. It is of interest to note 

 that the Cainpanulacere, which were also examined, have water-stomata 

 of the ordinary type, and are destitute of a cutinised membrane. The 

 author is uncertain as to the exact physiological meaning of these new 

 stomata, but believes that their early and complex formation points to 

 some important function in connection with the early life of the leaf. 



Lenticels of Palms. J — G. L. Gatin has studied the development of 

 the lenticels found upon the roots and at the base of the rootlets of 

 certain palms. The author finds that these structures are also found on 

 the petiole of the cotyledon of several distantly related species. They 

 are not confined to plants reared artificially, but may also be found on 

 those growing under natural conditions. They develop where the hypo- 



* Rev. Gen. Bot., xix. (1907) pp. 169-92 (5 figs.), 

 t Tom. cit., pp. 305-16 (1 pi.). 

 % Tom. cit., pp. 193-207 (13 figs.). 



