8 C. E. Beecher — Origin and Significance of Spines. 



first normal leaves, which are followed by others more and 

 more toothed and bristly, until the leaf is represented by a 

 branching spine, while finally spines only are formed. The 

 Spondylus represents a progressive increase in growth to pro- 

 duce the spines, while the Barberry exhibits a progressive 











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Figures 7-12. — Diagrams showing growth and differentiation of ornament into 

 spines. 7, surface with parallel lines ; 8, surface with regular reticulate lines ; 

 9, same, with spines developed at the points of intersection; 10, same, with the 

 vertical lines obsolete, but still represented by the vertical rows of spines; 11, 

 same, with the horizontal lines obsolete, but still represented by the horizontal 

 arrangement of the spines; 12, same, with all lines obsolete, but both series 

 represented by the vertical and horizontal arrangement of the spines. 



decrease of growth, or an " ebbing vitality," as it has been 

 termed by Geddes. 20 



The spines are the final results of both the direct and indi- 

 rect modes of production ; the direct, through a process of 

 building on new tissue, and the indirect, through a process of 

 dwindling away to all but the axial elements. These dif- 

 ferences are graphically expressed in figures 13 and 14. 



Attention should be called to the four kinds of spine pro- 

 duction in different organisms. (1) In the Radiolaria, Echi- 

 noids, the Giraffe, Cattle, and the Rhinoceros, the spines or 

 horns are persistent, and grow by additions to the original 

 structure. The new tissue may be superficial, subterticial, 

 interstitial, or formed by synchronous resorption and growth. 

 (2) In the Crustacea and Articulata generally, and in the Deer, 



