54 



COMPENDIUM OF GENERAL BOTANY. 



dition is found useful in all of the three forms of epidermal 

 function. If the contiguous radial walls of the epidermis take a 

 wavy course (whereby their area is also increased), it very materially 

 increases the mechanical resistance to the separation of the contact- 

 walls. In an actual test rupturing of the tangential outer wall 

 took place much more readily than separation of the radial contact- 

 walls. 



The accompanying figures show two small portions of represent- 

 ative epidermal tissue in surface view. 



FIG. 32. 



FIG. 33, 



In Fig. 34 are shown all three epidermal peculiarities quite 

 well developed. Let us consider it more in particular. The genus 



Aloe comprises plants adapted to with- 

 stand dry periods ; therefore they have 

 ? those anatomical features which tend 

 to reduce the loss of moisture well 

 developed. The cuticle inclusive of 

 the cuticular layers (cs = cuticular 

 layers, c = cuticle, b = cellulose) is 

 very thick. The cuticula is a thin 

 membrane highly impermeable to 



-Epidermal cells of the water> j t re8U lted from fatty and 

 waxy deposits in the cellulose-mem- 

 brane (cuticularization). In many of our indigenous plants this 

 cuticula is exceedingly thin, but is present in all plants; in sub- 

 merged water-plants it is almost reduced to zero (No. 2). 



The thickness of the entire outer wall inclusive of the thickened 



FIG. 34. 



leaf of Aloe acinacifolia. 

 (After Haberlandt.) 



