THE GROWING POINT 



279 



leaves the elaboration of plant-food takes place. Intercellular 

 spaces filled with air and other gases are common in this 

 tissue of leaves, as well as in parenchyma of other parts of 

 the plant. 



473. To study growing points use the hypocotyl of Indian 

 corn. Prepared slides may be secured having stained longi- 

 tudinal sections of the hypocotyl. The median section should 

 be studied with the high power. Note these points (Fig. 

 448) : (a) Root-cap beyond the grow- 

 ing point. (6) The shape of the end 



of the root proper and the shape of 

 the cells found there, (c) The group 

 of cells in the middle of the first 

 layers beenath the root-cap. This 

 group is the growing point, (d) Study 

 the slight differences in the tissues a 

 short distance back of the growing 

 point. There are four regions: the 

 plerome, several rows of cells in the 

 center; the endodermis, composed of 

 a single layer on each side; the peri- 

 blem, of several layers outside the 

 endodermis; the dermatogen, on the 

 outer edges. Make a drawing of the 

 section. If a series of the cross-sec- 

 tions of the hypocotyl should be made 

 and studied, beginning near the growing point and running 

 back some distance, it would be found that these four tissues 

 become more distinctly marked. The central cylinder of 

 plerome will contain the ducts and vessels; the endodermis 

 remains as endodermis; periblem becomes the cortex of 

 parenchyma; the dermatogen becomes the epidermis of the 

 root. 



474. Epidermal Tissue is a special modification of 

 parenchyma, comprising the thin layers on the exterior of 



gen; p, p, periblem; e, e, en- 

 dodermis; pi, pierome; i, in- 

 itial group of cells, or growing 

 point proper; c, root-cap. 



