PART II. 



THE ARRANGEMENT OF 



THE 



FORMS OF TISSUE. 



FIRST SECTION. 

 PRIMARY ARRANGEMENT. 



Sect. 54. The different forms of tissue result from the differentiation of the 

 primary meristem present in the growing points, and have a definite relative position 

 and arrangement. In very many instances this is permanent, as is the case in leaves, 

 and in the stems and roots of plants not belonging to the Dicotyledons and Gymno- 

 sperms. In other cases, especially in the last-named plants, either new structures, 

 which arise from secondary meristems, are formed, in addition to the tissues 

 derived from the primary meristem (p. 4) ; or changes, which are consequences of 

 secondary formations, appear in the primary tissues. 



The masses of tissue directly derived from the primary meristem and their 

 arrangement are called primary to distinguish them from those of later secondary 

 origin, and from consecutive secondary changes. We shall here study, in the first 

 place, only the first category. It is, it is true, to be expected a priori, that the 

 development of the primary masses of tissue takes place not suddenly, but in 

 definite succession, and that the secondary changes may be closely connected with 

 it, without there being any sharp limit between the two processes. Nevertheless in 

 many typical cases a definite limit between them can be found, and, from these as a 

 starting-point, it can be extended to all. 



The course of treatment in this section has been generally indicated by the 

 distinctions drawn in the first part. Of the forms of tissue there distinguished, the 

 epidermis will naturally not be treated of further. Its arrangement can be concluded 

 from Chap. I. i : also the arrangement of single parts of it, which should properly 



