200 



PLANT STUDIES 



ravages of animals (see §105). Examine Figs. 17G, 177, 

 178, 179, 180, 181. 



142. Anatomical adaptations. —It is in connection witli 

 the xeropliytes tliat some of tlie most sti'il\ing aiuitomical 

 adajotations liave been 

 developed. In such 

 conditions the epider- 

 mis is apt to he cov- 

 e r (' d ]) y 1 a y e r s (j f 

 cuticle, which are de- 

 veloped by the walls 

 of the epidermal cells, 

 and being constantly 

 formed beneath the 

 cuticle, may lieconie 

 very thick. This 

 f(ii'nis a very etiieient 

 2ir()te(;tive covering, 

 and lias a tendency to 

 diminish 1lic loss cf 

 Avater (sei' §•!•')). It is 

 also to be observed 

 that among xerophytes 

 there is a strong de- 

 velojimont of palisades 

 tissue. 'J'lie working 

 cells of the leaves next 

 to tlie exposed surface 

 are ehmgated, and are 

 directed endwise to 



the surface. In tliis way oidy the ends of the elimgated 

 cells are exjHised, and as sudi cells stand very closely to- 

 gether, there is no di-ying air l)et\veen them. In some 

 cases there may Ijc more than one of these palisade rows 

 (see §32). It has been observed that tlie chloroplasts in 

 these palisade cells are able to assume various positions in 



a. 



i. 177. Two pliiiit^ »if comnKiii gnr^e or furze 

 (fV'.r), allowing tllu effect of eiiviroiinient ; /) 

 is iL ])l:nit grown in moist conditions ; u is a 

 l)lant ^^rown iti diy conditions, tlie ]eil\'cs anil 

 branches having been almost entirely developed 

 as thorns.— After LOTiiELiEn. 



