CHAPTER XXX. 



STRUCTURE OF THE SEED OF ANGIOSPERMS. 



MATERIALS USED. 



Flowers and seed-pods of various ages of the Shepherd's Purse (Capsella 



Bursa-pastoris). March to November. Fresh, also in alcohol. 

 The same of the Water-Plantain (Alisma Plantago). June to August. 

 Ripe seeds of the Castor Oil plant (Riciniis communis). 

 Ripe grains of Wheat. Fresh ; slightly softened, or, preferably, just ripe. 

 Germinated Wheat ; fresh. 



REAGENTS USED. 

 Potash Carbolic acid. 



Dicotyledonous Seed of Capsella. We will now endeavour to 

 become acquainted with the structure of a ripe seed, and to give 

 especial attention to the embryo which it contains. As a com- 

 paratively favourable plant, we select one of the Cruciferae, 

 Capsella Bursa-pastoris, the shepherd's purse, a plant which 

 has been very largely used for embryological studies. Its seed 

 is comparatively small, but offers special advantages for de- 

 velopmental investigation. For this reason, therefore, we will 

 endeavour to overcome the difficulty which cutting it presents. 

 It is advisable first to prepare a median longitudinal section 

 through the seed, as we wish to know what the object looks like 

 the development of which we are about to study. If we have 

 fresh seeds at our disposal this section offers no insuperable 

 difficulty to preparation between the fingers. It is still easier 

 if we place the seed between two flat pieces of cork, and draw the 

 razor between them. Or the seed can be fastened with gum in 

 the desired position between two pieces of soft lime or poplar 

 wood ; and after it is dry the sections made through wood and 

 seed at the same time. Or the seed can be embedded in a drop of 

 gum, to which a little glycerine has been added, at the end of a 



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