STKUCTUEE OF THE SEED. 17 



VII. DEVELOPMENT OF OVULES. 



In this examination the wall of the ovary must be removed, 

 and the minute eminences which are to become the ovules ob- 

 served in their earliest stage. The successive external produc- 

 tions which are to become the integuments of the ovule should 

 be traced with great care. It is also well to examine minutely 

 the changes in form of the embryonal sac in the nucleus (or 

 nucellus) of the ovule. These will be further adverted to under 

 " Fertilization." 



VIII. MINUTE STRUCTURE OF THE SEED. 



Since in the previous exercises some parts of the seed have 

 been alread}' examined, it is necessary here merely to call atten- 

 tion to the desirability of studjlng the character of the integu- 

 ments in at least two common and a few exceptional cases. 

 For the former, no seeds are better than those of the common 

 Bean, Pea, or Lupine. After a clear idea has been obtained of 

 the nature of the cells which compose the greater part of the two 

 integuments, the student should make careful sections through 

 the hilum in order to display the peculiar sac-like body there 

 seen. For the exceptional types of integuments, examine the 

 seeds of Flax (showing the gelatinous modification, etc.), or 

 better, if they can be procured, the seeds of Collomia and Cot- 

 ton. It will be well also to examine the closely united ovarian 

 and ovular coats in the common grains, like Wheat or Indian 

 corn. 



The student should examine as many seeds as possible, includ- 

 ing those containing much, little, and no starch, and observe also 

 whether or not there is any difference between ripe and unripe 

 seeds in the amount of starch which the} T contain. He should 

 examine the contents of the cells nearest the integuments in any 



*- 



of the seeds above mentioned, and ascertain the relative amount 

 of albuminoid matters present compared with those in the cells 

 in the interior of the seed. 



Further microscopic examination of the seed is to be taken up 

 when germination is studied. 



