438 SUMMARY OF CUKRENT RESEARCHES RELATING TO 



gives rise to parenchyma, which in turn gives rise to phloem ; finally a 

 sclerotic core appears. There is an ill-defined internal endodermis. 

 There are large leaf -gaps through which the internal tissues successively 

 become continuous with the corresponding outer tissues. This seems to 

 show that the protostele gives rise to the ectophloic siphouostele, which 

 then develops into the solenostele or amphiphloic siphouostele with 

 large leaf -gaps. The cortical tissue does not intrude into the stele, and 

 the central tissue is complete before it joins the homologous external 

 tissue through a leaf -gap. The author concludes that both cortex and 

 medulla are fundamental tissue, and that while we have only to consider 

 two kinds of tissues, vascular and non-vascular, the vascular system has 

 a definite developmental history both in phylogeny and ontogeny. 



Differentiation of Tissues in Equisetum.* — C. Queva contributes 

 a note upon the differentiation of wood and phloem in Equisetum. The 

 procambial strands appear as isolated groups of small cells, and in each 

 strand the phloem is formed before the xylem. The differentiation of 

 the xylem is exclusively centrifugal, the protoxylem being mostly repre- 

 sented by a lacuna, around which are the remains of the primary tracheids. 

 A second formation of wood continues this centrifugal differentiation to 

 right and left. This metaxylem may, like the protoxylem, l^reak down 

 and form lacunar, e.g. the lateral lacuna in the rhizomes of E. limosum 

 and E. littorale. The vascular bundles of Eguisetum must not be 

 regarded as simple and unipolar, since there are thus two directions in 

 which the wood is differentiated. 



Anatomy of North American RubiaceaB.j — T. Holm has studied 

 the Rubiaceffi of North America, including Cephalanthus, Houstonia, 

 Galium, etc. The author notes the following epharmonic characters : 

 (1) In the roots : some genera have no exodermis, others have a super- 

 ficial development of cork inside the exodermis, while in others there is 

 a thick-waUed cortical parenchyma ; (2) In the stem : Cephalanthii.s has 

 a stereome ; there is great variation in the development of collenchyma 

 in the different genera. {?■>) In the leaves : some genera have bifacial 

 structure, while others have isolateral structure ; the distribution of the 

 stomata varies ; some species of Galium have epidermal resin-cells ; the 

 epidermis and cuticle vary ; some genera have glandular hairs ; the 

 palisade tissue varies in distribution and development ; some genera 

 have water-storage tissue in the leaves. Finally, the author confirms 

 the family characters as given by Vesque and Solereder. 



Stem-thickening in Euterpe oleracea.J — H. KranzHn has in- 

 vestigated the stem of Euterpe, and finds that it grows in the same way 

 as other palms, but tliat a new feature presents itself. In a stem which 

 has a diameter of 5" 5 cm., and is already woody, there is a layer of 

 meristematic tissue around the vascular bundles, which multiplies until 

 a thickness of about thirty cells is reached. The stem at this time 

 is about 10 cm. in diameter. Even during cell-multiplication, and 

 for long after, there is progressive radial stretching and wall-thickening 



* Comptes Rendus, cxliv. (1907) pp. 862-3. 



+ Bot. Gazette, xliii. (1907) pp. 153-86 (3 pis.). 



X Ber. Deutsch. Bot. Gesell., xxiv. (1906) pp. 483-9 (4 figs). 



