CLASSIFICATION OF THE PRIMORDIA 



109 



It is rather difficult to find an explanation of obliquity. A 

 priori three possibilities exist : 



(i) The observed obUquity is merely an illusion due to a 

 quincunxial disposition of the segments. 



(2) ObUquity is a consequence of an obUque position of the 

 cell-walls in each longitudinal row. In certain leaves of 

 Bryum argenteum I have observed that several longitudinal 

 rows are sometimes regular and parallel, the transversal cell- 

 walls bemg oblique (Fig. 17). Each row resembles a ladder 

 with obUque rounds. This curious disposition being Hmited to 

 a small part of the leaf, it may be supposed that obUquity is 

 here secondary, the ceU-walls being obUque, the simple axes 

 being rectangular. 



(3) It is conceivable that an obUquangular system reaUy 

 exists. This would be obtained if the divisions were succeed- 

 ing each other alternately, for instance, in the directions NS 

 and SE-NW. In this case the axes 

 of both kinds would be in reality 

 lines of segmentation, gradation and 

 differentiation. I could not find 

 any example of this supposed 

 obUquangular biaxial system. The 

 determination of the exact direction 

 of the nuclear spindles might throw 

 some light upon this question. 



Curious examples of obUquity are 

 observed in the shells of certain 

 Mollusca and are mentioned as 

 specific characteristics ; for instance, in certain species of Tellina 

 (T.fabula), Pecten, etc. (In these shells a rectangular system is 

 ordinarily predominant, the axes being anticUnal and pericUnal.) 



§ 87.— REMARKS ON THE BIAXIAL SYSTEM (CHESS- 

 BOARD SYSTEM, §§ 77-86). SIMPLE PROPERTIES.— 

 When we want to discern and to measure the primordia of a 

 given biaxial system we ought before aU to estabUsh the direc- 

 tion of the axes and the existing alterations ought to be deter- 

 mined. After this preliminary work the primordia (simple 

 properties) are measured in the direction of each axis, as if each 

 of both axes existed alone. In other words, ihe whole system 

 ought to be regarded as a compound of two independent uniaxial 

 systems. The primordia of each system may be enumerated 

 and classified according to the scheme in § 57 (see also §§ 60, 

 72. 73. 78), each primordium being measured separately. 



It happens very often that two or more alterations exist simul- 

 taneously in a given system. Since the possible alterations 

 may coexist in the most various ways, numerous combinations 



Fig. 17. — Bryum argenteum. 

 Cells of the leaf. (Schematic) 



