74 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS 



diameters for the earliest ones and ten or less for the later ones. Some 

 of the sections may be treated to advantage with potash solution and 

 acetic acid (Sec. 169). Note the changes in size and shape of the seed, 

 in relative development of seed coat and embryo, and in relative bulk 

 of the style, stigma, and ovary wall (pod) compared with the' contained 

 seeds, as the latter mature. After treatment with potash, several steps 

 in the development of the embryo can be made out with m.p. Note 

 that when the developing seed is not more than J to } the length of the 

 mature (dry) seed, its interior is mainly embryo sac, with a rudimen- 

 tary enibryo at one end. Make several drawings to show stages in the 

 process by which the embryo grows until it fills the sac. 

 C. If fresh material can be had, cut off under water the stalk to which 

 some well-grown pods are attached. Transfer the stalk (without 

 exposing the newly cut surface to the air) into eosin solution and allow 

 it to stand for an hour or more in a warm, sunny place. Cut trans- 

 verse and longitudinal sections of the pods as soon as they appear well 

 stained along the edges, and slice off thin layers from the flat surface 

 of a pod. Sketch the distribution of the fibro-vascular bundles (recog- 

 nized by the stain) in all the sections. 



Eefekence. Strasburger-Hillhouse, 6. 



