492 



THE SPECIFIC CONSTITUTION OF PROTOPLASM. 



a mycelium which has penetrated the bark and wood of a Beech-tree, grows 

 the horse-shoe-shaped ashen-gray Polyporus fomentarius to mention but a few 

 of the commonest forms. 



The fruits resulting from the conjugation of the unicellular Desmids are 

 minute balls of protoplasm, and although they may originate from very different 

 species, outwardly there is not the slightest distinction between them. But as 

 soon as these small balls of protoplasm begin to develop, the greatest variety 

 of cell-forms is the result. Each is fashioned after the form of the parent in- 

 dividuals which produced the fruit by conjugating. One cell will be half- 



Fig. 356. Desmidiese. 



i Micrasterias papillifera. 2 Micrasterias morsa. 8 Cosmarium polygonum. * Xanthidium aculeatum. 5 Staurastrum 

 furcatum. Euastrum oblongum. 7 Penium Brebissonii. 8 Closterium Lunula. 9 Xanthidium octocorne. 10 Staur- 

 astrum alternans (two views). n Cosmarium tetraophthalmum. 12 Aptogonum Desmidium. All the figures magnified 

 about 200 times. 



moon-shaped, another cylindrical, a third angular and table-shaped, others again 

 stellate and with manifold projections; some have a smooth surface, while the 

 cell-wall of others is beset with spines or studded as if with pearls. The figures 

 above, representing twelve different species of these Desmids, will give some idea 

 of the multiplicity of their forms. And all these varieties spring from apparently 

 identical masses of protoplasm, and develop side by side in the same drop of water, 

 under the same illumination, the same temperature, and, generally speaking, under 

 exactly the same external conditions and stimuli. 



All these observations and results seem to indicate that the hypothesis as 

 to a specific constitution of the protoplasm in each species is almost a necessary 

 assumption. The word " constitution " has been purposely used instead of " com- 

 position", which might be taken to mean essentially the same thing were we 



