8 LECTURE I. 



tributed. It occurs comparatively rarely that, as in the case 

 of the zoospore of Haematococcus, all these properties are 

 exhibited by the protoplasm of one cell. 



Haematococcus and Saccharomyces are good examples of 

 those lowly-organised plants in which the individual consists of 

 a single cell; and yet, simple as is their structure, they present 

 a distinction of parts, in other words, they exhibit differentia- 

 tion. In the resting Haematococcus and in Saccharomyces 

 we can distinguish between protoplasm and cell-wall, and in 

 the Haematococcus-zoospore between the part of the proto- 

 plasm which is granular and coloured green and that which is 

 hyaline and is produced into the cilia. It is possible, there- 

 fore, to imagine that still simpler forms might be met with, 

 forms entirely undifferentiated, and this is in fact the case. 

 In certain Fungi (Myxomycetes), for example, cells occur 

 which consist merely of a minute mass of colourless and ap- 

 parently homogeneous protoplasm. We are forced to conclude 

 that in such an undifferentiated unicellular individual, all its 

 functions are performed by all parts of its protoplasm alike, 

 for there is no indication that any one part of it is especially 

 charged with the performance of any one particular function. 

 In a differentiated unicellular plant, however, there is an 

 adaptation of certain parts of the protoplasm to the perform- 

 ance of certain functions ; thus in Haematococcus and in 

 Saccharomyces the peripheral layer of the protoplasm is espe- 

 cially concerned in the formation of the cell-wall, and in the 

 zoospore of Haematococcus the cilia are the parts of the proto- 

 plasm which effect the movement of the organism. In the 

 more highly organised unicellular plants, such as Vaucheria 

 and its allies, the differentiation is carried still further: in those 

 which are green, for instance, the colouring-matter is not dis- 

 tributed throughout the protoplasm but is associated with 

 certain specialised parts of it, forming with them the chloro- 

 phyll-corpuscles; further, we find that in many cases the func- 

 tion of reproduction is performed by certain parts of the cell 

 only. In ascending, then, from the lowest to the highest 

 unicellular plants we find that whereas in the simplest forms 

 all parts of the cell appear to be equally concerned in all the 



