Morphologie, Teratologie, Befruchtung, Cytologie. 483 



leaves or roots respectively to be carried outwards by the growth 

 in depth of the cortex. the outer part of which increases also in 

 superficial area as the leaf- and root-bases respectively enlarge. It 

 is argued that the form of the stele in the caulome and the crescent- 

 shaped expansion of it at right angles in the basal part of the stock 

 are in agreement with the view that the stock of Isoetes is composed 

 of a shoot and rhizophore, for which the nearest analogy in the 

 vegetable kingdom seems to be found in the Lepidodendreae , since 

 in the Ferns and Eqiiisetum the root-sj^stem of the mature plant 

 consists of adventitious roots and the rhizophores of Selaginella are 

 very different. At the same time it is pointed out that the comparison 

 so often made between the lobes of the stock of Isoetes and those 

 of Pletironieia and the Lepidodendreae is fallacious; it is the root- 

 producing groove of the lower, supposedly rizophoric part of the 

 stock that corresponds morphologically to the lobes of Pleuronieia. 

 One of the principal objections to such a view is that the 

 secondary meristem at the base of the cauline stock seems to be 

 continuous with the deeply seated growing-line of the rhizophore 

 and in some cases this cauline meristem actually contributes to an 

 upward extension of the horns of the rhizophoric portion of the 

 vascular tissue. These facts undoubtedly suggest a relation between 

 the growing point of the rhizophore and the secondary meristem 

 of the shoot; but they do not prove that the rhizophore is merely 

 a peculiar secondary growth and offer no explanation of the 

 exceptional method of growth and root-production. It is even sug- 

 gested by the author that the cortical extension in Isoetes, which 

 is usually assumed to be due to a secondary meristem is a con- 

 tinuation throughout life of the increase in depth of the cortex 

 found in the growth of all roots and shoots, and made more 

 conspicuous by the small vertical elongation of the axis. In support 

 of this view it is claimed that older root- and leaf-traces are stretched 

 throughout their whole course and not only at the level of the 

 cambium, that cortical extension is seen in young plants, still devoid 

 of a secondary meristem and that it continues in those in which 

 there is practically no secondary growth. 



Isabel Browne (London). 



Lang, W. H., "Studies in theMorphologyof Isoetes. II. The 

 Analysis of the Stele of the Shoot of Isoetes laaistrts i n 

 the light of Mature Structure and Apical Development". 

 (Mem. Proc. Manchester Liter. Philos. Soc. Vol. 59. Part II. 

 van. 1915.) 



The author has carefully investigated and accurately re-described 

 the structure of the stele of Isoetes. Apical growth seems to proceed 

 from a small group of cells, or possibly occasionally from a Single 

 cell. There is in the stem a central, purely cauline mass of xylem 

 intermingled with parenchymatous cells, upon which the leaf-traces 

 are inserted. Between the projections formed by the latter and 

 broken by them is a sheath of radially seriated xylem, primary in 

 origin, but varying in degree of development. Beyond this peripheral 

 xylem is a small parenchymatous sheath and a layer of primary 

 phloem continuous with the phloem of the leaf-trace. Hofmeister 

 and more recently Stokey failed to recognize this layer, holding 

 that there was no primary phloem in the stem. The anomalous 

 secondary growth, so often described for Isoetes, takes place by the 



