TYPE STUDIES, SEED PLANTS 183 



What can you say of the economic importance of the family ? Make 

 a list of all the cultivated BosacecB that you know and state for what each 

 is valued. Uses of some wild species ? 



165. Family Leguminosae. The black locust (Robinia Pseudacacia), one 

 of the vetches (Vicia or Lathyrus), or the common pea (Pisum) are good 

 types for study. 



Robinia Pseudacacia. 



A. Sketch a well-grown tree (best before the leaves appear). 



B. Examine the roots for tubercles. In the locust, as iji the Leguminosx 

 generally, these serve an Important purpose in manufacturing soluble 

 nitrogen compounds for the use of the plant. 



C. Sketch a twig to show the arrangement of the thorns. 



1. What are the thorns ? How related to the winter buds ? Why ? 



2. Are the twigs mature and alive to their tips ? How is the growth of 

 the twig continued in the spring ? What other trees or shrubs do 

 you know with the same characteristics ? 



8. Cut off a large branch of locust. Is there much distinction between 

 sapwood and heartwood ? For what is the wood most valuable ? 

 What other woods are notable in the same way ? 



D. Sketch a locust leaf. 



1. Is the number of leaflets constant ? 



2. Study and report on the positions of leaves on horizontal and vertical 

 twigs. Explain. 



3. Study the leaflet position : (o) on outer branches in sunlight ; (6) on 

 inner branches or in dull weather ; (c) at night. 



4. Sketch a leafy twig as seen in positions of (a), {&), and (c). Explain 

 the use of each position. 



Try to ascertain by studies 'of the leaves on the tree what 

 percentage of the noon illumination on a perfectly sunny day is 

 necessary to produce position (a) and what to produce posi- 

 tion (6). (For method of measuring relative intensities of illumina- 

 tion see Exp. XXVIII.) 



E. Note the time of appearance of the flowers relatively to that of the 

 leaves. Is it the same in all individuals ? In southern Italy the 

 flowers usually appear before the leaves. Advantage of this ? 



1. Sketch a twig with a flower cluster in its natural position. 



2. Sketch an entire flower and another dissected. Why is a flower of 

 this shape called papilionaceous ? 



3. Make a diagram of the longitudinal section. 



4. Make a detailed drawing of the longitudinal section of a large flower 

 bud, two to four times natural size. Show plainly the beard of 

 hairs below the stigma. 



