96 THE QUANTITATIVE METHOD IN BIOLOGY 



II. In a chess-board system x gradation may be observed in 

 one of the directions NS or EW, or in both directions at the 

 same time (§ 82.) 



III. In a similar way gradation may be 

 observed in the intermediate units (seg- 

 ments) %+i,jc+ 2, . . . alluded to. (Sub. I.) 



IV. In a chess-board system differentia- 

 tion may occur. (§ 83.) 



V. In a similar way differentiation may 

 be observed within the limits of the inter- 

 mediate units x^-\, x+2, etc. 



VI. In a chess-board system one axis or 

 both axes may be ciirved lines. (In reality, 

 a curved axis consists of a succession of very 

 short, straight axes.) (§ 84.) 



VII. A diess-board system may become 

 irregular, its constituent segments being in 

 disorder. (§ 85.) 



VIII. A rectangular chess-board system 

 may be altered by the existence of oblique 

 axes (false axes ?) in the plane NS-EW. 

 (§ 86.) 



§80.— ALTERATIONS OF THE 

 CHESS - BOARD SYSTEM (continued). 

 INTERMEDIATE UNITS.— The epidermis 

 \. of the interior surface of a scale of an onion 

 bulb {Allium cepa) consists of one layer of 

 cells, which are united into a chess-board 

 system x. We observe a segmentation into 

 a number of segments a; + 1 following each 

 other in the direction EW (transverse direc- 

 tion) . Each segment x+x (longitudinal 

 row) is segmented in its turn into unicellular 

 segments x + z according to the direction 

 NS. The longitudinal rows % + i are indi- 

 viduals intermediate between the epidermis 

 considered as a whole and the cells. In 

 each longitudinal row the limits between 

 the cells are independent by their position 

 of those in the adjacent rows — in other 

 words, each row has its own independent 

 scale of a bulb. Four segmentation. The cells are ahnost always 

 '^^^%.r' longer than broad. 



^ In this example the properties are dis- 



tributed in a different way according to both axes. This 

 difference is, moreover, expressed by &e fact that the resist- 



F1G.9. — Allium cepa. 

 Epidermis x of the 

 interior surface of a 



