70 The Ottawa Naturalist. [Aug. -Sept. 



become spherical and thus reducing their contact surfaces to 

 nearly nil (Loewi, Fitting, Hannig). Or it ma}' be a result of 

 chemical alteration (a) of a part or (b) of the whole of the cell 

 wall. The middle lamella may be dissolved, in this way loosening 

 the secondary walls from each other; or the whole or part of the 

 secoiidary membrane ma_v be altered (Tison). Such chemical 

 alteration may or may not be preceded by cell-division in the 

 cells directly involved. lEven in species in which this usually 

 takes place, it may be omitted (Tison, Loewi) either entireh^ or 

 in a part of the separation layer, as I have myself observed. 

 When cell-division does occur, it is an expression of a resumption 

 of growth (secondary meristem of previous authors), but as cell 

 growth obviously does not necessarily lead to cell-division, this 

 may be absent. The amount of growth may vary with external 

 conditions, and it is ustially much more marked under water or 

 when high relative humidity prevails, and may lead to callus 

 hypertrophy (Kuster, 40, p. 289). And in species where growth 

 is usually omitted (e.g., Ampclopsis, Impatiens) cell-division 

 accompanying separation is still occasionally observable. 



Rhexolysis, while frequent in the mosses, is, so far as I know, 

 generally quite rare, and its precise nature and the causes leading 

 up to it need investigation. Tison believes it to occur in Aristo- 

 lochia SipJio (leaf), but Loewi questions the accuracy of Tison's 

 observations,' basing his criticism on the similarity of Tison's 

 description and drawings to appearances seen by him (Laurus, 

 etc.), and leading to separation by the joint action of chemical 

 alteration in the cell-wall and turgor. In view of my own work, 

 Loewi's criticism is justified. 



An apparently true case of rhexolysis, however, occurs in 

 the style of Gossyphim. Several minute transverse fissures 

 appear at different levels somewhat above the apex of the ovary. 

 These deepen and gape. Microscopically, they are seen to pass 

 transversely through the tissues without relation to the position 

 of the cell-walls, and without any evidence of separation of 

 entire cells. The protoplasts, with their inclusions, are found 

 in situ and the protoplasm torn through. Experiments indicate 

 that external mechanical relations (pull or pressure of the 

 staminal tube) are not factors. The fissures are not to be 

 discovered before the latter half of the second day of anthesis. 



Schizolysis is, on the other hand, general, but presents 

 widely divergent appearances. The simplest cases (primary 

 meristem) are those in which, by the solution of the primary 

 meml)rane (middle lamella), the involved cells — usually occupy- 

 ing an ill-defined and irregular zone — can fall apart. Loewi, 

 assigning to alteration of the membranes a very minor role, 

 believes that separation, as exemplified in Ampelopsis, is accom- 



