PAKENCHYMATOUS TISSUE 



253 



the growing point. In the mesophyll (or middle soft 

 part) of leaves the elaboration of plant-food takes place. 

 Intercellular spaces filled with air and other gases are com- 

 mon in this tissue of leaves, as well as in parenchyma of 

 other parts of the plant. 



410. To study growing points, 

 use the hypocotyl of Indian corn 

 which has grown about one -half 

 inch. The material should be placed 

 in 40 per cent alcohol for a few 

 hours, then in 70 per cent for the 

 same length of time, and then in 95 

 per cent until ready for use. Make 

 a series of longitudinal sections, 

 stain with hematoxylin, mount, and 

 then select the middle or median 

 one for study with the high power. 

 Note these points (Fig. 395): (a) 

 Root-cap beyond the growing 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 beneath 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 endo- 

 dermis, composed of a single layer on each side ; the 

 periblem, of several layers outside the endodermis, and 

 the dermatogen, on the outer edges. Make a drawing of 

 the section. If a series of the cross -sections of the hypo- 

 cotyl 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 



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

 dodermis; pi, plerome; i, init- 

 ial group of cells, or growing 

 point proper; c, root-cap. 



