ZOOLOGY AND BOTANY, MIOBOSCOPY, ETC. 267 



Formation of Centrifug^al Thickenings in the Walls of Hairs 

 and in the Epidermis.* — H. Schenck has carefully investigated the 

 mode of thickening of many epidermal structures, with the view of 

 testing whether it is best explained on the basis of Nageli's theory of 

 intussusception or Strasburger's of apposition. His general con- 

 clusion is that the external projections on cell-walls are some- 

 times the result of foldings which are afterwards filled up by 

 apposition, sometimes of growth by intussusception, though using 

 the term in a somewhat different sense from that of Nageli. Among 

 the structures examined were the hooks on the hairs of the fructifica- 

 tion of Marsilea, the hollow hairs on many plants which subsequently 

 become filled up, the hairs on the nodes of Coleus, the epidermis of 

 petals, and many others. 



Mechanical Sheaths to Secretion receptacles-f — K. Mobius de- 

 scribes the mechanical protections sometimes found in schizogenous 

 intercellular resin-passages, as in the leaves of Pinus and in the 

 adventitious roots of PMlodendron. They consist of one or more 

 layers of elongated cells with sclerenchymatously thickened walls. 

 The arrangement occurs in several different forms, which are described 

 in. detail. Less striking instances occur in the primary cortex of 

 the ivy, the periphery of the leaf-stalk of Angio^teris, and elsewhere. 



Curvature of Ovules-t — P. Van Tieghem proposes to define more 

 accurately than has hitherto been done, the exact mode of curvature 

 of anatropous and campylotropous ovules ; the terms suggested are 

 taken from those already used in describing the unsymmetrical 

 development of leaves. Van Tieghem proposes to call an anatropous 

 or campylotropous ovule Jiyponastic when the curvature is in an upward 

 direction, epinastic when in a downward direction, exonastic when the 

 curvature is horizontal towards the median nerve of the side of the 

 upper face of the carpel, endonastic when the curvature is horizontal 

 towards the edge of the carpel. These specialities are often cha- 

 racteristic of the whole of large natural orders ; sometimes of special 

 tribes or even genera within an order. 



Sexual Characters in Zinnia, § — T. Meehan remarks on the 

 change of sexual character which follows the change of a tubular to a 

 ligulate floret in Zinnia, Dahlia, and he believes all composite flowers. 

 In Zinnia a single ligulate floret would often be surrounded by 

 tubular and hermaphrodite ones ; but it would have the purely 

 pistillate character of the ray florets. In like manner when in the 

 double BaJilia the tubular florets become ligulate, the neutral 

 character of the ray florets follows with them. It is evident that in 

 these cases there is an intimate connection between the form of the 

 floret and its sexual character. 



* Schenck, H., ' Unters. iiber d. Bildung von centrifugalen Wandverdickungen 

 an Pflanzenhaaren u. Epidermen.' Bonn, 188i, 42 pp. (1 pi.). See Eot Zta- 

 xlii. (1884) p. 733. ' 



t "Vers. Deutsch. Naturf. u. Aerzte Magdeburg, Sept. 20, 1884 See Bof 

 Centralbl., XX. (1884) p. 62. 



J Bull. Soc. Bot. France, xxxi. (1884) pp. 67-70. 



§ Pioc, Acad. Nat. Sci. Philad., 1884, p. 210. 



