36 BOTANY 



parently solid granules are really small vacuoles filled with soluble 

 substances, like the tannin-vesicles of Zygnema; or these small 

 vacuoles may themselves enclose small solid granules. 



Vacuoles. There are found in most plant-cells cavities of greater 

 or less extent, filled with watery fluid, and known as Vacuoles. 

 They are always bounded by a layer of hyaloplasm, much like the 

 limiting outside portion of the protoplast. It has been found possi- 

 ble to kill the surrounding cytoplasm by means of a solution of 

 nitre, leaving the film of living hyaloplasm about the vacuole. 

 Under certain conditions the vacuoles have been observed to divide, 

 and it has been assumed that the film of hyaloplasm surrounding the 

 vacuole differs from the rest of the cytoplasm, and the name Tono- 

 plast has been given to it, under the supposition that, like the nu- 

 cleus and plastids, the tonoplasts are integral parts of the cell, and 

 can never arise de novo. This, however, has been shown not to be 

 the case, and there seems no question that vacuoles may arise free 

 in the cytoplasm, and form about themselves a layer of hyaloplasm, 

 without any reference to preexisting tonoplasts. 



Protoplast of Schizophytes. The lowest plants are the Schizo- 

 phytes, comprising the Bacteria, and the Blue-green Algse. There 

 is much controversy as to the structure of the protoplast in these 

 forms, especially in the Bacteria, which often show an apparently 

 homogeneous protoplast. In the larger forms a so-called "central 

 body " is often present, and may perhaps represent a primitive form 

 of nucleus. It has been claimed that in many Bacteria nearly the 

 whole protoplast is composed of such a central body, the outer cyto- 

 plasm being almost entirely absent. 



Protoplast of Typical Plants. The protoplast of the typical plant- 

 cell shows a nucleus and one or more plastids or chromatophores. 

 The latter appear in the young cells of the growing-point of a 

 stem, or in the cells of an embryo, as minute colorless granules, 

 usually in the neighborhood of the nucleus. These may remain 

 colorless, or they may develop into the green chloroplasts, or the red 

 or yellow chromoplasts. Fungi show no chromatophores, and they 

 are unknown in the cells of animals, unless some of the Flagellata 

 with chromatophores are admitted to be animals. 



Physical Constitution of Protoplasm 



During the past twenty years the structure of the protoplasm has 

 been the subject of most assiduous study, and great advances have 

 been made in the methods of fixing and staining the protoplasm in 

 order to differentiate its different components. In spite of these 

 studies, and the numerous ingenious theories propounded to explain 



