276 PLANT FAMILIES: DICOTYLEDONS. 



pairs. The ovary is divided- into four lobes, and at the 

 maturity of the seed these form four nutlets. The leaves are 

 rounded, crenate on the margins, the lower 

 ones petioled and heart-shaped, and the upper 

 ones sessile and clasping around the stem 

 beneath the flower clusters. From the clasp- 

 ing character of the upper leaves the plant 

 derives its specific name of amplexicaule. The 

 Fig. 237- plant occurs in waste places and is rather 



Diagram of lamium r 



flower, common. 



Of the two exercises given below one may be omitted. 



Exercise 79. 



438. The catnip (Nepeta cataria). — While the "dead nettle" is used 

 here to illustrate the mint family other species may be studied instead. The 

 exercise is written for the catnip (Nepeta cataria), * very common weed 

 occurring from July to September. If fresh material is not at hand when the 

 study is made, dried entire plants, and the flowers in formalin may be used, 

 unless it is preferred to use fresh material of some other available species. 

 In that case the dead nettle here illustrated, and the exercise, will serve as a 

 guide for the study. 



The entire plant. — Note the habit, the character of the branching, the 

 shape of the stem, the character of the surface. Note the form and arrange- 

 of the leaves. Is the plant annual, biennial, or perennial ? 



The inflorescence. — What is the inflorescence ? The flower ; the parts 

 present, the calyx, form and relation of parts ; the corolla ; form, relation of 

 parts ; into what two parts is the corolla divided ? the name of the two parts ? 

 the number of petals in each part ? Note the stamens, number, size, position 

 in the flower. The pistil ; sketch a pistil showing the nutlets, the long style. 



To study the stamens remove a corolla, split it open down one side and 

 spread it out on a glass slip and mount in water ; or pin it to a cork. Ex- 

 amine with a good hand lens, or with the lower power of the microscope. 



Construct the floral diagram. 



Cross-pollination by insects. — Study the adaptations of the flower for this 

 purpose. The lower lip is the landing place, and the upper lip is the "ban- 

 ner. ' ' If there are color markings on any portion of the flower which serve 

 to guide the insect in entering the flower, describe them and note the location. 

 With a needle imitate the entrance of an insect into the flower and determine 

 the way in which cross-pollination takes place. 



