380 STRUCTURE AND LIFE HISTORIES 
sterile region with foliage-leaves, and the restriction of the 
sporophylls to the apices of the branches is of very con- 
siderable advantage, making possible an abundant supply 
of food to a vast number of spores. The branching of 
L. Selago is dichotomous, and the sporangia are borne 
on the upper surfaces of the sporophylls, near their bases. 
339. The Gametophyte. The spores of Lycopods are 
alike in size (isospores), and on germination produce 
fleshy prothallia, bearing both antheridia and archegonia 
(monoecious), and partially saprophytic in habit. They 
commonly have a filamentous fungus growing parasitic- 
ally within their tissues. The reproductive organs occur 
at the upper end, surrounded with sterile hairs (para- 
physes). The whole of the antheridia, and the venters of 
the archegonia are imbedded in the vegetative tissue. 
The gametophyte may grow more or less completely im- 
bedded in the soil, but when growing on the surface chloro- 
phyll is formed, and photosynthesis may take place. Its 
lower end bears numerous rhizoids. 
340. The Embryo. After an egg is fertilized it begins 
at once to divide and soon develops an embryo. Of the 
two cells resulting from the first division of the fertilized 
egg, the lower one serves as a suspensor, while the other 
becomes the ancestor of all the cells of the embryo. The 
suspensor serves to push the embryo down into the nour- 
ishing tissue of the prothallus. The young embryo 
(Fig. 275) soon becomes differentiated into two distinct 
regions-^-the foot (not shown in the figure), and the shoot. 
As in the mosses and true ferns, the foot serves to absorb 
nourishment from the gametophyte. But the embryo is 
dependent upon the gametophyte for only a relatively 
brief period shorter than in the mosses and true ferns. 
