DEVELOPMENT OF PLANTS 279 



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 differentiation that is much more extensive 

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

 tionship with the mosses. The germination of the gametospore 

 gives rise to a rather cylindrical or pod-shaped body (Fig. 199). 

 The basal portion of the sporophyte develops into a massive foot, 

 often provided with rhizoidal-like outgrowths, which serve as a 

 very efficient absorbing organ. The upper portion of the sporo- 

 phyte 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 alternating with sterile cells which in some genera develop 

 as elaters. In the center of the sporophyte is a mass of sterile 

 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 sporophyte 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. 



It is evident that this sporophyte would become a self-support- 

 ing plant if its foot should reach through the gametophyte and 

 absorb substances from the soil. In comparing the sporophyte 

 in forms like Ricciocarpus, Marchantia and the leafy hepatics 

 with Anthoceros, we see that it has undergone a gradual evo- 



