1892.] MICKOSCOPICAL JOURNAL. 107 



bark-producing function in the epidermis, due to inlieritance point- 

 ing backward to the time when the epidermis of this stem was an 

 aerial organ of the phmt. 



The bud is also covered with epidermis, but the cells like all 

 those of the bud are embryonic. They are small, more globular, 

 and filled with protoplasm. They are alive and capable of growth 

 and secretion, keeping pace with the general development of the 

 bud. The bud shows hardly any cell differentiation at its outer 

 parts, though the tissues of the potato are formed at its base, but 

 the cells show subdivisions into terminal and lateral portions and 

 leaves even in the most embryonic specimens. It would be very 

 interesting to inquire into the state of the living protoplasm in the 

 dormant bud. Only a little warmth and moisture applied 

 during a few days are necessary to arouse the vitality of the pro- 

 toplasm and cause the bud-cells to rapidly grow by division and 

 acquire the various functions of new stems. 



Directly below the epidermis there are flat cells, but much 

 thicker than those of the outer skin. These cells are protoplasmic 

 and alive. They can be readily seen in both vertical sections or 

 horizontal sections. If these cells be treated with a dilute acid, 

 as I per cent, hydrochloric or nitric acid, the protoplasm will be 

 coagulated and shrunken, and then a thin layer of it which form- 

 erly fitted closely the cell-wall becomes visible (see fig. 5). The 

 layer is called the primordial utricle. Its function is to secrete 

 and shape the cell-wall. The primordial utricle in a living cell 

 is so close to the cell-wall that in a living cell it can be seen only 

 rarely, and only by the best trained observers. The central mass 

 of protoplasm can be seen in the living cell (see fig. 3, e) with its 

 nucleus and radial streams of protoplasm stretching between the 

 centre and the primordial utricle. The protoplasm is thus in- 

 sufficient to fill the cell ; the spaces left are called vacuoles and 

 contain watery fluid. 



In embryonic cells which have not attained maturity of size and 

 structure, the protoplasm fills the cell (see fig. 3, d^ ; there are no 

 vacuoles. It is in cells at the layer e of figure 3 that the starch is 

 being formed. In all the other parts except just here, next the 

 epidermis, the process has been completed. This makes it pos- 

 sible for the potato to constantly enlarge during its season of growth. 

 The drawings in figures 6, 7, and 8 show portions of difterent 

 cells very highly magnified. The protoplasm is shown surround- 

 ing the nucleus with its well marked nucleolus. Scattered about 

 in the protoplasm, but chiefly in the immediate vicinity of the 

 nucleus, can be seen numerous minute droplets of starch. They 

 present the features of starchy degeneration, a state which some- 

 times happens as a pathologic change in animal protoplasm and 

 which also closely resembles the mode of occurrence of fatty" de- 

 generation in the senile yeast-cell and in unhealthy animal cells. 

 The droplets formed increase by addition of increments of starch 

 until a number of very well-defined starch-bodies can be seen, usu- 



