136 Plant Biology 



vegetative stem and (2) the colorless, unhranched, fertile, reproductive 

 stem with its single, terminal cone. 



Sporangia (five to ten in number) are borne on a sporangiophore 

 which is shield shaped or umbrella shaped. Numerous sporangiophores 

 are grouped to form the cones (strobili). The spores are alike (homo- 

 sporous), and each has four ribbonlike, hygroscopic elaters (el'ater) 

 (Gr. elater, driver) which are affected by moisture changes to assist in 

 the movement of the spores. A germinating spore forms a small, green, 

 ribbonlike young gametophyte, with rhizoids, and usually with both male 

 antheridia and female archegonia. The spiral, multiflagellated sperms 

 swim to the archegonium where the egg is fertilized to form a zygote. 



•v-i^-;,.,^^>».;..i;rj;/-- 



D 



E F 



Fig. 48. — Smaller club "moss' (Selaginella) of the phylum Tracheophyta, class 

 Lycopodineae. A, Part of a mature sporophyte ; B, strobilus (from tip of branch) 

 consisting of numerous sporophylls, each with a basal sporangium ; C, micro- 

 sporangium (in section) producing small microspores; D, microsporangium (in 

 section) in which biflagellated sperms (antherozoids) are produced from mega- 

 gametophytes, the latter having developed from microspores; E, megasporangium 

 (in section) producing large megaspores; F, archegonium (in section) with its 

 egg, in a megagametophyte, and a sperm about to enter; a megaspore (within 

 the megasporangium) germinates to form a megagametophyte which contains 

 archegonia (with egg, etc.) ; a fertilized egg forms a zygote from which develops 

 the parasitic, embryonic sporophyte; G, older sporophyte (still attached to the 

 megagametophyte) bearing embryonic, primary stem, leaves, and roots. 



