144 LABORATORY AXD FIELD EXERCISES 



the text. Cut thin transverse sections of young and 

 mature portions of stems of any cultivated geranium or 

 of a similar herbaceous stem. 



a. General features. Do the stem sections of the geranium 



correspond to the summary of the herbaceous stem 

 structure of Salvia ? Do you find tissue layers in 

 the stem sections of geranium not present in Salviai. 

 If so, what are they and in what main tissue zone 

 do they occur, epidermis, cortex, vascular cylinder, 

 or pith ? 



b. Secondary growth by cambiums. Compare transverse 



sections cut from young and mature portions of the 

 stem of a geranium. What differences do you find 

 between the young and the mature stem sections ? 

 Locate both the cork and the vascular cambiums, 

 and the secondary tissues produced by them. Does 

 the geranium plant produce corky bark ? Examine 

 both the sections and the surface of old portions of 

 geranium plants concerning this point. 



c. Leaf gaps and leaf traces. Study sections cut through a 



node or just below it. Do you find interruptions, or 

 gaps, in the vascular cylinder where the leaf trace 

 is given off ? Large branch gaps may also be found, 

 caused by an outgoing branch. Do you think that 

 the irregular contour of the vascular ring is caused 

 in part by leaf gaps and branch gaps ? 



d. Tissues of the vascular ring. Compare these with those 



of the spruce just studied. Do you find wood rays? 

 annual-growth rings ? wood parenchyma ? Compare 

 the ducts with the tracheids of spruce. 



e. Storage tissues of lite gerctnhtm stem. Determine the 



places where starch is stored in sections treated 

 with iodine. 



