CHAPTER XLIII. 



THE VEGETATIVE SYSTEM OF VASCULAR PLANTS 



ANALYSED. 



A MOST effective factor in the higher development of the sporophyte is 

 the continuance of apical growth. In some few cases this is absent, as 

 in the sporogonium of certain Liverworts, and the development is then but 

 small ; or intercalary growth may intervene as in the Jungermanniaceae, 

 and be continued for a long period, as in the Anthoceroteae ; but in all 

 the more elaborate cases, including the Mosses and all Vascular Plants, 

 localised apical growth is effective, though it is usually associated with 

 intercalary growth. This localised and continued apical growth is 

 taken up early by the apex of the axis in the young embryos of 

 Vascular Plants, and is persistent through life : it is by reference to the 

 simpler cases where it does not exist that its importance as a factor in 

 the organisation of the plant-body will be duly appreciated. In presence 

 of the sporophytes such as those of the Liverworts it becomes evident 

 that apical growth is not a general factor in the neutral generation : it 

 seems probable that in the first instance it did not exist, and that the 

 whole sporophyte owed its origin to a primary, intra-archegonial embryo- 

 geny : that localised apical growth, and as a consequence continued 

 embryogeny, was acquired as a secondary development, though it has 

 become a dominating influence in all the more elaborate sporophytes. 



The mode of segmentation which accompanies apical growth provides 

 important material for comparison, according as it is conducted with a single 

 initial cell or with many, and according as the meristem is stratified or 

 not. In certain cases comparison leads to the conclusion that the more 

 definite segmentation with a single initial is a derivative state in the 

 sporophyte, and that with several initials the more primitive. Among the 

 Bryophyta there is no distinctive evidence on this point : the sporogonia 

 of the Musci have as constantly a single initial cell as those of the Hepaticae 

 have none. But among the Pteridophyta evidence of value comes from 

 the Filicales, and also, though less clearly, from the Lycopodiales. A 



