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 Fic. 392. — Lycopodium complana- 
aggregation or strobilus. In ‘um, showing vegetative branches and 
such forms it is obvious that clusters of terminal strobili (X 3). At 
there are two distinct kinds of _ the left of the strobili is an enlarged 
leaves—sporophylls and vege- view of a sporophyll showing the spor- 
P : .  angium. Below the sporophyll are 
tative leaves. In intermedi-  .hown some sooies: highly dawmihed: 
ate forms one can find sporo- Redrawn from Britton & Brown. 
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. 
PITT 
