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On the Structure of Mucilage Cells. [June 16, 



commences by the breaking down of a portion of the innermost layers 

 of the endoplasm at a number of contiguous but isolated areas. The 

 result of these katabolic changes in the protoplasm is the formation of 

 small but rapidly growing mucilage drops. The first formation occurs 

 just beneath the free surface, and takes place equally around the 

 whole cell cavity, and the phenomenon steadily continues from within 

 outwards, producing new drops basipetally, and immediately beneath 

 those already formed, until the whole of the endoplasm, together with 

 the substance of the plastids (or starch grains), have taken part in 

 the process, and the cell is now full of isolated drops, each enclosed 

 by a portion of the delicate protoplasmic framework which still 

 remains. 



A remarkable sequence of changes occurs in the drops themselves. 

 At their first formation they are watery and by no means well defined. 

 By the use of osmic acid it can then be. shown that they contain no 

 tannin. They shortly become denser, and at this stage tannin appears 

 equally distributed throughout their structure. And now in the 

 drops themselves a delicate reticulation maybe observed, which finally 

 gives way to the appearance of numerous minute and brightly shining 

 droplets, all separate and distinct, disseminated through the substance ♦ 

 of the drop, just as the drops themselves are disseminated through 

 the substance of the protoplasm. Reactions show that the ground 

 substance of the drops is of the nature of a gummy mucilage, while 

 the drops consist of pure gum. Our observations make us disposed 

 to believe that during secretion the protoplasm gives rise to a gummy 

 mucilage, and the latter undergoes further differentiation into a 

 ground substance which still retains its mucilaginous character, and 

 into a gummy substance (a product probably of maximum chemical 

 change) which is present as a number of isolated spherical droplets. 

 In the light of these remarks the structure presented by the mature 

 cell becomes more clear. 



In the case of many animal glands, e.g., serous and mucous salivary 

 glands, Langley concludes that the protoplasm forms the hyaline 

 substance, and then out of this manufactures the granules, which 

 during secretion are turned out of the cell and give rise to the parti- 

 cular substance which the gland secretes. The state of active secre- 

 tion is followed by a resting period during which the protoplasm 

 grows, forms new hyaline substance, and this again produces new 

 granules. We believe that a series of changes essentially similar in 

 character occurs in plant cells also. Usually speaking, plant cells are 

 incapable of such active and repeated secretion as occurs on those of 

 animals, and in many cases, e.g., Blechnum and Osmunda, the secretion 

 changes occur in the cell once and for all, and at their termination the 

 cell dies. In other instances, however, e.g., the glands of Dioncea, it 

 appears exceedingly probable that the phenomena which accompany 



