378 



BOTANY. 



Dicksonia growing in the Sandwich Islands constitute the substance 

 known as Pulu, used somewhat in upholstery. Many of the species 

 are now largely grown as ornaments. 



Ferns first appeared in the Devonian, in which period no less than 

 twelve genera belonging to extinct families were represented. In the 

 Carboniferous the genera and species were exceedingly numerous, after 

 which they decreased to the present. Many Tertiary genera extend to 

 the present, and are now represented by living species. 



Order Marattiaceae, the Ringless Ferns. The prothallia of the 

 ringless Ferns are thick, fleshy, and dark green in color. They bear 

 antheridia in depressions upon both surfaces, and in these are pro- 

 duced spermatozoids bearing much resemblance to those of true Ferns. 

 The archegonia are also deeply sunken in the tissue of the prothallium, 

 and, according to McNab, resemble those of the Rhizocarpese. 



The asexual generation bears a close resemblance to that of true 



N 



FIG. 268. 



PIG. 269. 



Pig. 268. A prothallium of Botrychium Lunaria, in longitudinal section, ac, an 

 archegonium ; an, an antheridium near to it are others, one not yet mature, and 

 three empty ones ; w, root-hairs, x 50. After Hofmeister. 



Fig. 269. A longitudinal section of the lower part of a young plantof the same, dug 

 np in September, st, stem ; b, b', b", leaves, x 20. After Hofmeister. 



Ferns. The plant-body is usually large ; its stem is generally upright, 

 short, thick, and unbranched ; the leaves are circinately developed, as 

 in true Ferns, and are mostly very large, with pinnately or palmately 

 divided laminae ; they are provided with stipules, and in their petioles 

 is found the first collenchyma. The stem develops from a three-sided 

 apical cell, but the root is provided with a group of cells, as in the 

 Phanerogams. 



The sporangia occur on lateral veins upon the under side of the 

 leaves, and are usually confluent into one body, the sorus (often called 

 erroneously the sporangium). In Angiopteris, however, the sporangia 

 are distinct. The spores develop from many mother-cells in each spo- 

 rangium, instead of from one, as in true Ferns. 



The Marattiaceae are essentially tropical, extending somewhat into 

 the warmer parts of the temperate zones. Four genera are known, 

 viz. , Dan&a, restricted to tropical America ; Kaulfussia and Angiopteris, 



