126 BOTANY. 



The leaves in most species are like those of the larger club 

 mosses, but more delicate. They are arranged in four rows on 

 the upper side of the stem, two being larger than the others. 

 The smaller branches grow out sideways so that the whole 

 branch appears flattened, reminding one of the habit of the 

 higher liverworts. Special leafless branches (B, r) often grow 

 downward from the lower side of the main branches, and on 

 touching the ground develop roots which fork regularly. 



The sporangia are much like those of the ground pines, and 

 produced singly at the bases of scale leaves arranged in a spike 

 or cone (A, sp.), but two kinds of spores, large and small, are 

 formed. In the species figured the lower sporangium produces 

 four large spores (macrospores) ; the others, numerous small 

 spores (microspores). 



Even before the spores are ripe the development of the 

 prothalliuni begins, and this is significant, as it shows an 

 undoubted relationship between these plants and the lowest 

 of the seed plants, as we shall see when we study that group. 



If ripe spores can be obtained by sowing them upon moist earth, the 

 young plants will appear in about a month. The microspore (Fig. 74, K) 

 produces a prothallium not unlike that of some of the water ferns, there 

 being a single vegetative cell (#), and the rest of the prothallium forming 

 a single antheridium. The spermatozoids are excessively small, and 

 resemble those of the bryophytes. 



The macrospore divides into two cells, a large lower one, and a smaller 

 upper one. The latter gives rise to a flat disc of cells producing a number 

 of small archegonia of simple structure (Fig. 74, 7, J). The lower cell 

 produces later a tissue that serves to nourish the young embryo. 



The development of the embryo recalls in some particulars that of the 

 seed plants, and this in connection with the peculiarities of the sporangia 

 warrants us in regarding the Ligulatce as the highest of existing pterido- 

 phytes, and to a certain extent connecting them with the lowest of the 

 spermaphytes. 



Resembling the smaller club mosses in their development, 

 but differing in some important points, are the quill-worts 

 (Isoetece) . They are mostly aquatic forms, growing partially 



