11d. Vegetative Organs of Vascular Plants 



The vegetative organs of the vascular })lants are the leaf, the 

 stem, and the root. These organs can be studied either from the 

 standpoint of developmental morphology and histogenesis, or they 

 may be studied from the comparative viewpoint by a comparison 

 of the mature organ in its diverse forms. A combination of the two 

 viewpoints has much merit, and the following presentation of mate- 

 rials and methods affords suitable material for such studies. 



Meristems 



This section is limited to the apical meristems or growing points 

 of stems and roots and the associated organ primordia. Lateral meri- 

 stems are more properly discussed in connection with secondary 

 growth of older stems and roots. The study of the activities of meri- 

 stems is in part a study of mitosis. Some prepared slides of meristems 

 are intended to show critical details of mitosis; however, some slides 

 also are prepared to show tissue systems and organ primordia. For 

 either type of slide, meristematic tissues are processed by the most 

 critical methods that time and facilities permit. 



THE ROOT TIP 



Growing points of roots are obtainable from seedlings sprouted on 

 blotting paper, from sprouted bulbs, from older plants in pots, or 

 from plants dug up in the field. Regardless of the source or length 

 of a root, the meristematic region is confined to the terminal 1 to 2 

 mm. (Fig. 13.1). Penetration of reagents occurs over the entire sur- 

 face. For elementary work, adequate cellular detail is obtained with 

 the entire root tip. The pieces are thus large enough to be handled 

 easily. Longitudinal sections show the relationship of the root cap, 

 the meristem, and the older tissues, and slides can be made by 

 quantity-production methods. For more critical studies the root tip 

 should be cut into the smallest possible pieces or prepared by one 

 of the modern smear methods. The best of these methods have been 

 admirably assembled by Johansen (1940) and Smith (1947) . There 



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