SIZE OF OVULES 37 



ing the ovules shown in Figure 42 and those shown in Figure 38 

 the number of ovules in a Tomato may be roughly estimated. 



An examination of the ovaries of many plants would show 

 considerable variation in the number of locules and ovules, but 

 in general, all ovaries consist of an ovary wall enclosing one or 

 more locules which contain one or more ovules. 



Ovule. — Since ovules develop into seeds, they have the most 

 to do with seed production and are, therefore, the most directly 

 related to the function of the flower. The process of fertihzation, 

 one of the most important events in plant life, takes place in the 

 ovule and a good understanding of fertihzation requires a knowl- 

 edge of the ovule. 



Size of Ovules and how their Number Compares with the Num- 

 ber of Seeds. — Although ovules are the chief structures in per- 

 forming the function of seed-production, in size they are usually 

 very inconspicuous and not much can be learned 

 about them without the aid of the microscope. . 



In many plants the ovules are barely visible to j 



the unaided eye. When ovaries and ovules are ^ 



shown in drawings, they are usually much en- 

 larged, so that much more is shown than could ,^'°' *^' ~ ^^^^ 

 , , ,,. .. 1,1-,, of the Tomato taken 



be seen by cuttmg sections and studying the from the flower and 



ovaries themselves, unless a microscope were drawn natural size. 

 used. In Figure 43, the pistil of the Tomato is 

 shown natural size. By comparing it with the pistil shown in 

 Figure 4^, it will be seen that in order to show the structures of 

 the ovary, the pistil in the latter Figure is much enlarged. 



Since ovules are small, it is difficult to count them in ovaries 

 where they are numerous. It is possible in many cases to make 

 a rough estimate of the number of ovules by counting the seeds 

 produced. Since each seed is a developed ovule, there must 

 occur in the young ovary as many ovules as there are seeds in the 

 mature ovary. From this it follows that those Tomatoes con- 

 taining two hundred or more seeds must have had as many ovules 

 in their young ovaries. 



If all the ovules became seeds then a count of the seeds would 

 give the exact number of ovules; but in many cases, due to a lack 

 of fertilization, space, or sufficient food supply, only a part of the 

 ovules complete their development and become seeds. In Red 

 Clover, as shown in Figure 40, there are two ovules, but when the 



