746 THE AMERICAN NATURALIST. [VOL. XXXVIII, 



ate cells show some definite activity resulting in extensive growth 

 or peculiarity of form. Thus some laticiferous coenocytes are 

 branching tubes that grow for considerable distances among the 

 cells of the tissues in which they are contained. The embryo- 

 sac and the female gametophytes of Selaginella and Isoetes in 

 the early stages of their development are interesting coenocytes. 

 Among the lower algae there are numbers of cosnocytic forms 

 (e. g., Hydrodictyon, Cladophora) whose cells present very little 

 change with age except an increase in size. Yet some of these 

 conditions, especially those illustrated in the Cladophoraceae, are 

 probably related to the higher types of coenocytes. 



The best differentiated coenocytes are found in the Siphon- 

 ales, Mucorales, Saprolegniales and to a lesser extent among the 

 Peronosporales and are especially well illustrated in a few aquatic 

 forms, such as Monoblepharis and Myrioblepharis. The pecul- 

 iarities of these forms lie in elaborate structures which result 

 from the ability of the ccenocyte to respond to several directive 

 stimuli in its growth. The most complicated responses and con- 

 sequently the most highly differentiated morphology is shown 

 among the Siphonales, where some very elaborate forms are 

 found. In many types the plant body is clearly composed of 

 root and shoot regions and in the highest expressions (e. g., 

 some species of Caulerpa) there are rhizoids, shoots and leaf- 

 like structures presenting a remarkable degree of specialization. 

 The behavior of the protoplasm in these most highly differenti- 

 ated types of the Siphonales is known to us chiefly through 

 studies of Noll and Klemm. 



There is a very conspicuous layer of clear protoplasm next to 

 the cell wall which constitutes an outer plasma membrane (haut- 

 schicht). This outer plasma membrane is stationary while the 

 granular protoplasm within changes its position readily and fre- 

 quently in different portions of the plant streaming in various 

 directions. The nuclei are all situated in the granular cytoplasm 

 so that they must shift their positions with its movements. Noll 

 ('87) by a clever method' of coloring the cell wall of living plants 

 of Caulerpa was able to prove that the forward growth took 

 place by the protoplasm extending beyond the old wall, thus 

 adding new regions of cellulose to the old. He called this. 



