THE MORPHOLOGICAL COMPOSITION OF PLANTS. 25 



mechanical kind. The aggregate of them is scarcely more 

 individuated than a lump of inorganic matter : as witness the 

 way in which the lichen extends its curved edges in this or 

 that direction, as the surface favours; or the way in which 

 the fungus grows round and imbeds the shoots and leaves 

 that lie in its way, just as so much plastic clay might do. 

 Though here, in the augmentation of mass, we see a progress 

 towards the evolution of a higher type, we have as yet none 

 of that definiteness required to constitute a compound unit, 

 or true aggregate of the second order. Another kind 



of obscuration of the morphological units, is brought about 

 by their more complete coalescence into the form of some 

 structure made by their union. This is well exemplified 

 among the Confervoidece and Conjugates. In Fig. 18, there 



are represented the stages of a growing Mougeotia genuflexa, 

 in which this merging of the simple individualities into the 

 compound individuality, is shown in the history of a single 

 plant; and in Figs. 19, 20, 21; 22, 23, are represented a 

 series of species from this group, and that of Cladophora* in 

 which we see a progressing integration. While, in the lower 

 types, the primitive spheroidal forms of the cells are scarcely 

 altered, in the higher types the cells are so fused together 

 as to constitute cylinders divided by septa. Here, however, 



* It may be objected that in Cladophora the separate compartments of 

 the thallus severally contain many nuclei, making it doubtful whether they 

 descend from uni-nucleate cells. If, however, they do not they simply illus- 

 trate another form of integration. 



