480 LECTURE XXVIII. 



isolated from the remaining tissues, surround themselves with new cell-walls, and 

 after a period of rest develope into new plants. - 



All these phenomena of adventitious budding apparently stand in contradic- 

 tion to the previous statement that the formation of organs in the vegetable 

 kingdom proceeds from the embryonic tissue of the growing-point, which we have 

 in its turn regarded as a derivative from the embryonic substance of the fertilised 

 oosphere. But considerations from general points of view, to which I shall return 

 subsequently, render this apparent contradiction irrelevant; as the growing-points 

 which occur so universally are subordinated to the still more general conception 

 of embryonic tissue, so also this latter again may be looked upon simply as a 

 collection of embryonic substance formed during the process of nutrition in the 

 plant, and collected at definite spots according to circumstances in each case. 



In the cases of the adventitious formation of shoots and roots hitherto con- 

 sidered, it occurs in the particular species of plant at certain definite points, and 

 belongs moreover to the normal phenomena of life. At another opportunity, 

 however, and proceeding from other points of view, I shall have to show that 

 adventitious growing-points may arise at almost any given spot on the older 

 parts of plants, when these are cut off or injured, and that in this manner a new 

 shoot provided with roots may arise from the separated portions of shoots and 

 roots of many plants. It is better to reserve these phenomena for subsequent 

 consideration, however, since they serve to demonstrate particularly clearly the 

 influence of external forces on the production of new organs. 



