112 



BOTANY FOR BEGINNERS 



CHAP. 



watch glass. With a camel's hair brush mount the thinnest one in 

 water, and examine first with a low power then with the high power. 

 Note 



(i) The upper epidermis, a single layer of cells with an outer cuticle. 



(ii) The palisade parenchyma, which consists of cells, cylindrical in 

 form, with a few air spaces between them ; the chloroplasts are very 

 numerous in the cells. 



(iii) The spongy parenchyma, which consists of loosely-arranged 

 irregular cells with large air spaces between. 



(iv) The lower epidermis with the stomata. Each stoma opens into 

 a large intercellular space the air chamber. 



(v) That each stoma is a small opening between two guard-cells. 

 Each guard cell is sausage-shaped and curved, the ends of the guard- 

 cells being firmly joined together. 



(vi) The vascular bundles have the xylem above and \h& phloem below. 

 The xylem ends in the palisade cells and the phloem in the spongy 

 parenchyma. 



(vii) That the guard-cells contain chloroplasts, and that the other 

 epidermal cells have no chloroplasts. 



The Growing Point of the Shoot. The growing point 

 of the shoot consists of several layers of cells, which are meris- 

 tematic in character. These cells are 

 rich in protoplasm, and possess large 

 nuclei, and are in a constant state of 

 activity, i.e., growing and dividing 

 to form new cells. From this meri- 

 stem all the new tissues of the shoot 

 are developed. There are three 

 distinct layers of cells at the apex, 

 viz. : 



(i.) Dermatogen. On the outer 

 FIG. 139. Diagram of the grow- portion of the growing point a single 

 mftogl n n; 0f FR^W^em"; layer of cells is present. These divide 

 PL, plerome. ' U p by walls being formed at right 



angles to their surface. This layer 



gives rise to the epidermis of the young shoot, and is called 

 the dermatogen. 



(2.) Periblem. Below the dermatogen a layer of cells is 

 found, which, at the apex, may be only one layer of cells thick, but 

 lower down may be several cells thick. This is the periblem or 

 young cortex, for it forms the cortex. 



(3.) Plerome. Underneath the periblem is found a group 

 of cells, which gives rise to the whole of the vascular cylinder of 



