The nucleus is imbedded in a soft substance, which fills up the entire cell (Pl. I. fig. 2 _c_); this is the pro´toplasm (πρῶτς, first, πλἁσμα, formative substance). As it is very transparent, it is readily overlooked; but it may usually be shown distinctly by adding a little glycerine to the edge of the cover with a glass rod, when it contracts and separates from the cell-walls, as in the lower cell of fig. 2. The protoplasm in some cells is semisolid and of uniform consistence, while in others it is liquid in the centre, the outer portion being somewhat firmer and immediately in contact with the cell-wall. In the latter case, it forms an inner cell to the cell-wall, and is called the _primordial utricle_. The terms “protoplasm” and “primordial utricle” are, however, used by some authors synonymously. The protoplasm is the essential part of the cell, and it forms or secretes the cell-wall upon its outer surface in the process of formation of the cell considered as a whole. It is also of different chemical composition from the cell-wall, being allied in this respect to animal matter. _Chlor´ophyll_ (χλωρὀς, green; φὐλλον, leaf).--On examining a section of any green part of a plant, as the green substance of a Geranium-(_Pelargonium_-) leaf, it will be seen that the green colour does not arise from the whole substance being coloured, as appears to be the case to the naked eye, but from the presence of little grains or granules of a green colouring-matter in the protoplasm of the cells. This green matter is called chlorophyll. If the cells be crushed, the granules will escape, and can be examined in the separate state. Chlorophyll is most abundant in those parts of plants which are exposed to the light. _Starch._--In many cells of plants, particularly those which have attained their full growth, other granules, larger than those of chlorophyll, and colourless, are met with; these are the _starch-granules_ (Pl. I. fig. 3). They are usually rounded or oblong, and exhibit on the surface a number of rings, one within the other, or concentric, as it is called. In the centre of the innermost ring is a black dot or streak, arising from the presence of a little pit or furrow, and called the _hilum_. The starch-grains may be readily seen within cells in a thin section of a potato (Pl. I. fig. 4); here they are very numerous, and larger than in most other plants. A separate grain is represented in fig. 3. The appearance of rings in the separate grains arises from the starch-granules being composed of numerous concentric coats or layers, like those of an onion.