124 



MANUAL OF BOTANY 



inner layer. They thus originate in the periblem and not in the 

 plerome. 



The growth of the sporophyte from the oospore or zygote 

 shows considerable variety'. Epibasal and hypobasal segments 

 are produced, as in the Bryophyta, by the formation of a basal 

 wall. In the ferns and horsetails this is followed by segmenta- 

 tion into octants. From the epibasal octants the stem and either 

 one or two primary leaves or cotyledons are then produced, while 

 from the hypobasal ones proceed the primary root, and a foot 

 which, as in the Bryophytes, serves to attach the sporophyte to 

 the tissue of the gametophyte {figs. 880 and 881). The foot is 



Fig. 882. 



Fig. 882. Prothallium (gametophyte) of Peru. After Kuy. 



in this group a transitory structure, which perishes as soon as 

 the sporophyte is capable of an independent existence. In the 

 club-mosses the hypobasal segment gives rise to a suspensor, as 

 it does in Phanerogams (page 184). This is only composed of a 

 single cell, or a chain of a few cells in length. 



The gametophyte arises from the germination of the spore, in 

 most cases becoming free from it {fig. 882), but in certain cases 

 remaining partly or almost entirely in its cavity {fig. 883). In 

 the former case it is usually a small thallus composed only of 

 cells and containing chloroplastids. Its morphological character 

 is, however, varied ; it may be a filamentous much-branched 

 body, somewhat recalling a protonema, or it may be tuberous 



