SPOROPHYTE 



439 



Sporophyte. The sporophytes vary considerably in the dif- 

 ferent species, but consist of a stem simple or branched, bearing 

 numerous small leaves (Fig. 392). In numerous species com- 

 mon in temperate America the stems trail over the ground. 

 These species are often used for decorations at Christmas time 

 and are called Ground Pines, probably from the appearance of 

 their foliage, although they are not Pines at all. 



One of the notable features of the sporophyte has to do with a 

 suggestion as to the origin of 

 the strobilus. In the simplest 

 forms all leaves are alike and 

 sporangia occur in the axils of 

 the leaves on most any part 

 of the stem. These leaves do 

 the vegetative work and in 

 addition are sporophylls in so 

 far as they bear sporangia. 

 In the more advanced sporo- 

 phytes of Lycopodium only 

 certain leaves bear sporangia, 

 and these leaves differ consid- 

 erably in form as well as in 

 function from the other leaves. 

 They are located at the top of 

 the stem, forming the close 

 aggregation or strobilus. In 

 such forms it is obvious that 

 there are two distinct kinds of 

 leaves sporophylls and vege- 

 tative leaves. In intermedi- 

 ate forms one can find sporo- 

 phytes in which the leaves are 



all alike but some bear sporangia while some do not, and often 

 leaves bearing rudimentary sporangia can be found. These 

 facts have suggested that all leaves were at first spore-bearing and 

 that foliage leaves are sterilized sporophylls. According to this 

 theory, the simplest condition is one in which all leaves bear 

 sporangia, and the differentiation of foliage leaves and sporo- 

 phylls came about by sterilizing the leaves from below until the 

 spore-bearing leaves were finally limited to the top of the stem. 



FIG. 392. Lycopodium complana- 

 tum, showing vegetative branches and 

 clusters of terminal strobili (X ). At 

 the left of the strobili is an enlarged 

 view of a sporophyll showing the spor- 

 angium. Below the sporophyll are 

 shown some spores highly magnified. 

 Redrawn from Britton & Brown. 



