ANGIOSPERM^E. 425 



sis (h, Fig. 310, //., ///., IV., V.}. The growing points of 

 both root and stem develop in all cases from masses of 

 small cells, and never from single apical cells. 



The development of the embryo may be studied by selecting the 

 young ovaries of Capsella Bursa-pastoris, or Lepidium intermedium, and 

 dissecting out the ovules in a solution of potassic hydrate, aiid after- 

 wards transferring them to a solution of glycerine and water. Speci- 

 mens prepared in this way show clearly the embryo sac with the con- 

 tained suspensor and embryo when examined by means of a magnify- 

 ing power of from one hundred and fifty to four hundred diameters. 

 When they have been made too transparent by this treatment, their 

 walls may be rendered more opaque by the addition of a dilute solution 

 of alum. The young embryo may sometimes be separated from the 

 ovule by a gentle pressure upon the top of the cover-glass. 



534. The Endosperm. During the early part of the de- 

 velopment of the embryo, just described, the formation of 

 endosperm cells within the embryo sac takes place Avith great 

 rapidity ; in most cases the growth of the endosperm is so 

 great as to displace the greater part or even the whole of the 

 surrounding tissues. The cells of the endosperm contain 

 large quantities of nutrient matters, which are at first in so- 

 lution, but which later may pass into a less soluble condition. 

 The growing embryo is imbedded in the endosperm, and as 

 the former increases in size, the latter is displaced and ab- 

 sorbed. In many cases the growth of the embryo is arrested 

 before the endosperm is all absorbed e.g., in Eanunculaceae, 

 Violaceae, Solanaceae, Euphorbiaceae, Palmaceae, Liliaceae, 

 Gramineae, etc. ; in other cases the embryo continues to grow 

 until it has entirely absorbed the endosperm e.g., Cruciferse, 

 Rosacese, Myrtacese, Composite, Salicacese, Cupuliferae, 

 Alismacese, etc. 



535. The Perisperm. It rarely occurs that the endo- 

 sperm develops but slightly, and in such cases there is a con- 

 siderable development of the tissues of the ovule surround- 

 ing the embryo sac, constituting the perisperm ; in such 

 cases nutrient matters are contained in the latter, which 

 functionally replaces the endosperm. Examples of this 

 structure occur in Nymphaeaceas, Piperaceae, and Cannaceaa. 



536. During the growth of the embryo the ovule and 

 ovary undergo considerable changes. The outer coat of the 



