316 SUMMARY OF CURRENT RESEARCHES RELATING TO 



none open, although in two successive summers he investigated young 

 needles. The thickening on the cells of the stomatal apparatus in old 

 needles is such that any movement is improbable. 



Secondary Growth in Thickness in Palms.* — M. Barsickow has 

 investigated this subject in Phoenix reclinata, Phoenicophorium Seychella- 

 rum, Oreodoxa regia, and the Coco-nut. He confirms Eichler's view, 

 from all four example-!, that the subsequent thickening is caused 

 by enlargement of the cells of the wood-parenchyma. In Phoenix the 

 increase is due almost entirely to this, as both here and in Oreodoxa and 

 Phoenicophorium the sclerenchyma strands accompanying the bundles 

 increase only slightly in diameter. In the two latter, however, the 

 appearance of new intercellular spaces and the broadening of thoso 

 already present is an important factor. In coco-nut there is also a 

 considerable broadening of the bundle-sclerenchyma. This, however, 

 is due, not as Eichler thought, exclusively to a broadening and thicken- 

 ing of the fibres, but to a sliding growth caused by their growth in length. 

 Thus the lengths of fibres isolated by maceration from sections taken 

 at various heights above the root increased from 1*015 mm. at 14*5 

 inches above the root to 1*413 at 12 metres and 2*232 at 40 cm. above 

 the root, while their breadth at the same heights was '035, -037, and 

 •047 mm. respectively. 



Origin of the Peripheral Stem-Structure.f — F. Tobler concludes 

 that there is no satisfactory evidence that the peripheral layers of the 

 stem are derived from the leaf, but that, on the contrary, in Elodea and 

 other objects the cortex can be demonstrated to be an original stem- 

 structure. He maintains that arguments deduced from Conifers with 

 decurrent leaf-bases, in support of a leaf origin of the cortex are untrust- 

 worthy. In the Mosses and also in Equisctum the arrangement of the 

 cell-division at the growing-point favours the idea of an independent 

 origin. The author also shows that in Cirsium, and in Genista sagittalis 

 the wing on the stem has no genetic connection with the leaf. 



Origin and Differentiation of Vascular Meristems in the Leaf- 

 Stalk.:]: — M. Bouygues, as the result of investigations on a large series 

 of plants representing twenty families, concludes that in the majority of 

 leaves there are two sets of meristem which differ in time and place of 

 origin as well as in development. The first, which alone is constant, 

 forms an arc with concave side upwards. The differentiation of pro- 

 cambium strands and subsequently vascular bundles is always effected 

 there, and often there alone, but always before any such development 

 occurs in the other meristem. The bilateral structure of the leaf is 

 therefore primitive and fundamental. The second meristem is a cortical 

 one, situated above the former. The formation of vascular tissue in it 

 is not general; it fails at the base and apex of the leaf, and is absent 

 altogether in a large number of leaves. It frequently forms a plate 

 completing the vascular arc and transforming it into a closed circle 

 resembling that of the stem. 



* Verhandl. physik.-medic. Ges. Wiirzburg, N.F. xxxiv. No. 8 (1901) pp. 213-15 

 (1 fig.). t Pringsh. Jahrb., xxxvii. (1901) pp. 1)0-136 (13 figa. in text). 



; Compt. Rend., cxxxiv. (1902) pp. 438-41. 



