DEVELOPMENT OF PLANTS 293 



are sunken in the tissues. This arrangement doubtless protected 

 the reproductive organs just as did the involucre and perianth 

 in the preceding groups. 



The most suggestive variation of the Anthocerotales appears 

 in the development of the sporophyte. We have noted that the 

 asexual generation in forms like Ricciocarpus was a microscopic 

 plant consisting of a delicate spore-bearing capsule. In Mar- 

 chantia the sporophyte is still minute but differentiated into a 

 foot, stalk and capsule, and in the Jungermaniales this becomes 

 much more pronounced. In the Anthocerotales the sporophyte 

 assumes a growth and dififerentiation that is much more extensive 

 and complex and it also presents features that indicate a rela- 

 tionship with the mosses. Furthermore it shows certain features 

 in its development that also arose in the ferns. The germination 

 of the gametospore gives rise to a rather cylindrical or pod-shaped 

 body (Fig. 199), in which all the cells have become sterile save a 

 dome-shaped layer. The basal portion of the sporophyte de- 

 velops into a massive foot, often provided with rhizoidal-like 

 outgrowths, which serve as a very efficient absorbing organ. 

 The upper portion of the sporophyte presents a remarkable series 

 of differentiations. The outer part of it consists of chlorophyll- 

 bearing cells in which, for the first time, genuine stomata appear 

 (Fig. 199, ch). Within this zone of chlorenchyma is a dome- 

 shaped layer of spore mother cells often alternating with sterile 

 cells which in some genera develop as elaters. In the center of 

 the sporophyte is a mass of rather elongated cells, the columella, 

 which assist in conducting food from the foot to the forming 

 spores. Directly above the foot is a region of rapidly dividing 

 cells which causes the sporophyte to elongate by basal growth and 

 push out of the archegonium before the spores are mature. This 

 is a radical departure from the other liverworts in the mode of 

 development of the sporophyte and we will see essentially the 

 same manner of growth occurring in the mosses. As the sporo- 

 phyte develops, the spores in the upper part of it mature and the 

 sporophyte splits into two valves (Fig. 198, s'), thus permitting 

 the scattering of the spores. The lower portion, however, may 

 continue to elongate for several months in some species, forming 

 additional spores. 



