68 LABORATORY AND FIELD EXERCISES 



b. The structure of the ovule. 



(1) Gross structure. Dissect out the ovule from the 



ovary of some common plant into a drop of 

 water on a slide. Mount and observe the essen- 

 tial parts of the ovule ; namely, the f uniculus, or 

 stalk, the body of the ovule, and the micropyle. 

 Ovules of the shepherd's-purse (Capselld), when 

 treated with a weak solution of potash, will often 

 show the outline of the embryo sac within the 

 ovule. Draw one or more ovules to show the 

 structure observed. Label. 



(2) Microscopic structure of the ovule. If material is 



available, study thin sections cut through the 

 ovule to show the embryo sac and micropyle ; 

 for example, in shepherd's-purse or mandrake. 



(a) Determine the structure and thickness of the 

 seed coats. Do you see the micropyle of the 

 ovule ? What is the nature of the large cen- 

 tral light space of the ovule ? Is there a 

 nucleus in this space? Are there vacuoles 

 and cytoplasm ? Has this central space the 

 structures of a cell ? 



(1} Study the structure and position of the embryo. 



(c) Draw the sectional view of the ovule, indicating 

 the micropyle, the cellular structure of the 

 ovule coats, and the form and structure of 

 the embryo sac and embryo. 



POLLINATION IN PAPILIONACEOUS FLOWERS 



1. Inflorescence, or flower cluster. Examine an inflorescence 



of some plant belonging to the pea family. 

 a. Parts of the inflorescence. Has the inflorescence axis 

 the same parts as the stem axis below it; namely, 



