DEVELOPMENT OF THE SEEDLING PLANT. 591 



nucleus. If a nucleus be originally present, it disappears, or becomes as 

 it were liquefied in a mass of protoplasm which, from the admixture of 

 cell-sap, becomes frothy below, the upper portion becoming condensed and 

 granular. Around certain portions a cell- wall is formed as just explained. 

 Other portions of the protoplasm become liquid, forming the so-called 

 vacuoles. 



Development of vessels, epidermis, <Sfc. The different forms of 

 vascular tissue, including the laticiferous vessels, originate from 

 cells. The most usual course is for a number of more or less 

 oblong cells to range themselves end to end in longitudinal series ; 

 after a time the partitions between the cells are broken down or 

 reabsorbed, and a continuous tube results. The immediate inducing 

 cause, and the precise manner in which the partitions are absorbed, 

 are not known. 



The epidermal cells are in the first instance usually smaller than 

 the other parenchymatous cells, and more closely packed together. 

 They are at first spherical, or nearly so, but shortly assume the 

 usual flattened character. The epidermis is at first destitute of 

 stomata ; but these organs are gradually developed in the manner 

 described in the following paragraph. 



Development of Stomata. In certain of the cells the nucleus 

 previously in contact with the cell-well becomes detached from it, 

 and subdivides into two nucleoli ; the parent cell- wall then forms 

 a septum between them; and thus two cells are formed in apposition, 

 the septum being at first single, but subsequently splitting so as 

 to separate the two daughter cells and leave an opening (stoma) 

 between them which communicates with a wide intercellular space 

 beneath. Sometimes cell-division occurs in the above manner, 

 without the appearance of any nucleus ; but the parent and 

 daughter cells, unlike the other epidermal cells, always contain 

 chlorophyll. The intercellular canals, and canals for secretion, 

 originate in a similar manner to the stomata. 



Sect. 2. DEVELOPMENT or THE SEEDLING PLANT. 



The formation and mode of development of the embryo in 

 Phanerogamia will be hereafter alluded to. In this place it may 

 be well to allude briefly to the principal phenomena witnessed in 

 the germination of the embryo-plant. 



Germination of Dicotyledons. The germination of the embryo, 

 considered in its morphological aspect, begins by the protrusion of 

 the radicle (p. 156) in a downward direction, subject to very few 

 exceptions. The structure and formation of the growiug point 

 has already been alluded to. After the radicle has protruded, or 



