35 2 



PART IV. — VEGETABLE TAXONOMY. 



two-lobed or cordate at the apex, the growing point being located 

 between the lobes, and the middle portion of the prothallium 

 becomes several layered. The organ is usually better developed 

 and longer lived than in other vascular cryptogams. Except in 

 the Ophioglossums, where it is subterranean in its habit and 

 consists of a mass of chlorophylless cells of indeterminate shape, 

 it is a flat, green thallus, attached by one surface to the soil by 

 means of numerous simple root-hairs. m 



an 



Fig. 560. — A, under surface of prothallium of one 

 of the Polypodiacese, magnified about 25 diameters, 

 showing three archegonia, a, near the heart-shaped 

 apex, and farther back among the root-hairs, r, several 

 antheridia, an. 



B, an antheridium, magnified about 125 diameters, 

 showing cells, c, containing coiied antherozoids. j is 

 the cap-cell, which, when the antheridium is ripe, rup 

 lures to free the antherozoids. / is a portion of the 

 prothallium on which the antheridium is borne. 



C, is a ripe archegonium, also magnified about 125 diameters. /, portion of prothal- 

 ium in which the base of the archegonium is imbedded; g, germ-cell; «, neck of archego- 

 nium, consisting of four rows of cells; m mucilage discharged from neck. 



D, antherozoids, magnified about 500 diameters. 



The sexual organs of both sorts are borne on the inferior 

 surface. The antheridia are rounded bodies usually produced in 

 abundance at the margin and on the posterior surface of the 

 prothallium among the root-hairs. In the majority of cases they 

 consist of a single layer of cells enclosing other cells, which, by 

 division form the antherozoids. The antheridium when ripe 

 absorbs water, which causes it to burst at the apex, and the cells 

 containing the antherozoids are set free. Soon after, the walls of 

 these cells burst, each setting free an antherozoid which is coiled 



