INTRODUCTION 69 



the broken cj'linder (for details cf. Tschirch, 1885, p. 323 et seq., 

 and llaberlandt, p. 159). With respect to the ontogeny of osteo- 

 selereides and astroselereides, little information appears to exist. 

 In the husk of the fruit of hickory (Carya) a comparison of 

 young and old material clearly suggests that the irregular astro- 

 selereides arise much like brachysclereides from the secondary 

 sclerosis of parenchymatous elements. But the details of the 

 development of the huge astroselereides occurring in the leaves 

 of such plants as Camellia (Ilaberlandt, p. 162, Fig. 54) deserve 

 careful investigation. 



The statement is frequently made that stone-cells are devoid 

 of a protoplast at maturity. This idea requires further proof 

 because Alexandrov and Djaparidze (1927) contend that it is 

 possible to demonstrate, by staining with safranin and methyl 

 green, the presence of nuclei in the mature brachysclereides of 

 the fruits of quince (Cydonia) and pear (Pyrus). These inves- 

 tigators further maintain that during the ripening of the fruit 

 in Cydonia, the sclereides experience a process of " delignifica- 

 tion" consisting in the reduction in thickness of the wall, the dis- 

 appearance of lignin, and the obliteration of the ramiform pits. 

 This reversible change suggests enzymatic activity on the part of 

 the protoplasm within the stone cells. However, Crist and Batjer 

 (1931) reached a different conclusion in their detailed study of 

 the stone-cells of Pyrus. They state that the delignification re- 

 ported by Alexandrov and Djaparidze for Cydonia does not occur 

 in Kieff'er and Bartlett pears . . . ''without exception, the 

 downward trend of the cellulose curve is strictly parallel to that 

 of lignin and each one of the two is parallel to the ligno-cellulose 

 trend." Further study is obviously needed to determine more 

 precisely the chemical relations between the sclereides and the 

 neighboring parenchyma tissue during fruit ripening. 



From a functional standpoint, sclereides undoubtedly impart 

 hardness to the organ in which they occur. Haberlandt (p. 158) 

 states that brachysclereides "serve to increase the incompressi- 

 bility of the bark ; their action may be compared to that of the 

 sand which a mason uses to increase the tenacity of his mortar, 

 or to that of the powdered glass which is added to gutta-percha 

 in order to render it less compressible." The functional signifi- 



