THE MORPHOLOGICAL COMPOSITION OF PLANTS. 



17 



morphological units held together in one mass, becomes their 

 relative insignificance as individuals. We see this in the 

 irregularly-spreading lichens that form patches on rocks ; 

 and in such creeping fungi as grow in films or lamina? on 

 decaying wood and the bark of trees. In these cases, how 

 ever, the integration of the component cells is of an almost 

 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 struc 

 ture made by their union. This is well exemplified among 

 the Conferva, and their allies. In Fig, 18, there are re- 



Q 



presented 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 



