VISIBLE CONSTRUCTIVE ACTIVITY IN PROTOPLASM. 573 



threads, and a large quantity of dark spores which fill ujd the space inclosed bj' the 

 skin. Soon after, the skin breaks up into stellate projecting lobes at the free apex 

 of the spherical body, and now the dark spores can pour out of the open vesicle. 



The protoplasm of Didymium shapes itself quite diflerently, and that of 

 Clatroptychium ditierently again. If we were to exhaust the multiplicity of form 

 which the protoplasm of this gi-oup of plants assumes, we should be obliged here 

 to actually describe the shapes of all myxomycetes. The above examples will 

 suffice for the establishment of the fact that apparently quite similar protoplasm 

 becomes, in each species, speedily transformed into a definite structure. It only 

 remains to be noticed that the shape assumed by the specifically different proto- 

 plasm is quite independent of external conditions ; and that in the same light, with 

 the same degree of humidity, and at the same temperature, under the same glass 

 shade, the pear-shaped Leocarpus, and the cylindrical strands of Stemonitis develop 

 side by side (for illustrations of Myxomycetes cf. vol. II., fig. 355). 



The pellicle which bounds the plasmodia of myxomycetes contains no deposited 

 cellulose, and there is consequently in these plants generally no distinction 

 between the pellicle and the body of the cell. The protoplasm of other plants, 

 however, always provides itself, sooner or later, with an envelope in which cellulose 

 can be demonstrated. Of course, cellulose is often present in the cell-wall only in 

 small amount ; thus, in yeast, as well as in the majority of fungi, the main part of 

 the membrane is formed of nitrogenous compounds. Various phenomena lead to 

 the conclusion that by the development of cellulose in the skin, advantages are 

 obtained which are not enjoyed by myxomycetes, with their brittle pellicle built up 

 of firm nitrogenous compounds. The soft protoplasm is better protected against 

 injurious external influences by the cellulose wall, and the whole structure obtains 

 that firmness and strength which are absolutely necessary, especially to plants 

 composed of numerous cells. 



Moreover, the cell-wall must not be conceived as always a rigid covering, 

 as a chamber with immovable walls. In many instances it is rather to be 

 compared to the skin of an animal, which adapts itself to each alteration in 

 the shape of the body. In no case is the elasticity of the protojilasm hindei'ed 

 by the surrounding cell-wall. Frequently the cell-wall takes no share in the 

 visible plastic processes of the protoplasm which it incloses, and it usually perishes 

 when the transformations have been completed in the space it surrounds and 

 protects. In many instances, on the other hand, the outline and shape of the cell- 

 wall alter in correspondence with the alteration of the protoplasm inclosed by it. 



These remai-ks had first to be made in order to rightly understand the plastic 

 processes to be described successively as Segregation, Gemmation, and Cell Division. 



In the case of the Segregation associated with most of the previously described 

 Plasmodia, it is to be pointed out as characteristic that the protoplasm divides 

 within a rigid, enveloping cell-wall into completely separate portions of identical 

 shape, and develops no partitions continuous with the surrounding cell -wall. 

 The inclosing cell-wall stands in no direct contact with the formed protoplasmic 



