258 



SEEDLESS PLANTS 



Figure 493, called a prothallium. Examine one of these 

 bodies carefully with a lens. Observe that there are no 

 veins nor fibrovascular bundles, and the whole body of the 

 plant seems to consist of one uniform tissue. Some little 

 rootlike hairs, called rhizoids, will be found growing on 

 the under side, but these are shown by the microscope 



to be mere appendages 

 of the epidermis in the 

 nature of hairs, and not 

 true roots. Such a body 

 as this, in which there 

 is no differentiation of 

 parts, is what consti- 

 tutes a thallus. It 

 occurs in all kinds of 

 plants under varying 

 forms, and different 

 names are given to it. 

 In the ferns it is called 

 a prothallium. In them 

 it is generally short- 

 lived and is important only in connection with the work 

 of reproduction. Note its heart-shaped outline, and look 

 just below the deep notch at the apex for certain little 

 bottle-shaped bodies called archegonia. (They will prob- 

 ably appear under the lens as mere dots, or may not be 

 visible at all.) These correspond to the pistils of seed 

 plants. Lower down, among the rhizoids, or near the 

 margin of the prothallium, are certain organs, called antJie- 

 ridia, corresponding to the stamens of spermatophytes. 



493 494 



493, 494. — Prothallium of a common fern 

 {Aspidlum) : 493, under surface, showing 

 rhizoids, rk, antheridia, an, and archegonia, 

 ar; 494, under surface of an older game- 

 tophyte, showing rhizoids, r/i, and young 

 sporophyte, with root, w, and leaf, i (from 

 Coulter's "Plant Structures"). 



367. The Gametophyte. — The reproductive cells con- 

 tained in the antheridia and archegonia are called gametes 

 and from them the prothallium is called a gametophyte, or 

 gamete plant, in contradistinction to the sporophyte or 

 spore plant. The gametes differ from ordinary spores in 

 not being able to perform the work of reproduction directly 

 by germination, but a pair of them must first unite and form 



