Morphologie etc. — Varietäten etc. 645 



teils durch Periklinalteilungen der die Endodermis bildende Zell- 

 schicht aufgebaut. 



Die Einzelheiten der Kernteilungen müssen in der Arbeit nach- 

 gesehen werden. Jedesmal geht eine Literaturübersicht den eigenen 

 Untersuchungen voran. Th. Weevers. 



Stiles, W„ The Structure of the aerial Shoots of Psüotum 

 ßaccidum Wall. (Ann. Bot. XXIV. p. 373—387. PI. 25. 1910.) 



Psilotum ßaccidum resembles P. triquetrum in possessing some 

 secondar} T xylem and in being occasionally mesarch; the proportion 

 of leaves receiving vascular bundles would seem to be greater in 

 the former species. Moreover a leaf receiving a vascular supply 

 seems to be constantly associated with the bifurcation, though it 

 may be carried up on the stem above the bifurcation; this suggests 

 that the branching may be derived from an axillary form of rami- 

 fication. The leaf trace, when present, is very small and terminates 

 at the Insertion of the leaf; narrow elongated, unlignified cells not 

 found in P. triquetrum are, however, developed in the leaf of P. 

 ßaccidum and form a continuation of the vascular bündle. The spo- 

 rophyll constantly contains a vascular bündle which passes up the 

 axis of the sporangiophore, where it may consist of as many as 

 eight tracheides in transverse section; elongated parenchymatous 

 cells pass into the lobes of the sporophyll. This is strongly reminis- 

 cent of what occurs in Tmesipteris where, according to Miss Sykes, 

 the sporophyll bündle divides into three, the median bündle pas- 

 sing into the axis of the sporangiophore and the two lateral ones 

 into the lobes of the sporophyll. In P. ßaccidum, however, only the 

 elements of the median Strand are lignified. 



Boodle suggests that the mesarch condition of the stem is the 

 more primitive and that exarchy has arisen in connection with the 

 disappearance of traces; this is supported by a much marked case 

 of mesarchy occurring in connection with the insertion of a large 

 leaf trace of P. ßaccidum. 



The nature of the spore producing member is briefly discussed 

 and the conclusion is reached that the sporophyll is probably foliar; 

 that the sporangiophore is not, as Miss Sykes believes, a branch, 

 but that the evidence is insufficient to decide whether it is an organ 

 sui generis or foliar. Finally the author accepts the view that the 

 Psilotales are intermediate between the Lycopodiales an the Sphe- 

 nophyllales but nearer to the latter. Isabel Browne (London). 



Haeeker, V., Allgemeine Vererbungslehre. (Braunschweig, 

 Fr. Vieweg & Sohn. 2. verm. Aufl., m. Titelb., 133 Textf. u. 4 

 Taf., XII, 405 pp. 8°. 1912.) 



Die bereits nach Jahresfrist nötig gewordene 2. Aufl. hat in 

 mancher Beziehung verbessernde und ergänzende Aenderungen, 

 auf die Verf. einleitend näher hinweist, erfahren. Ohne auf Einzel- 

 heiten einzugehen, müssen wir uns hier darauf beschränken, die 

 Hauptpunkte des Buches kurz hervorzuheben. Nach einer histori- 

 schen Einleitung (1. Teil) werden im 2. Teil die morphologischen 

 Grundlagen der Vererbungslehre geschildert (Plasma, Kern 

 und Kernsubstanz, Chromosomen etc.); im 3. Teil die Weismann'- 

 sche Vererbungslehre und das Problem der Vererbung er- 

 worbener Eigenschaften (in Einzelkapiteln: frühere Erklärungs- 



