PTERIDOPHYTES 315 



consequence that the equisetum embryo, on account of the 

 prominence of the stem in the adult plant, forms as its promi- 

 nent organs a rudimentary stem, root, and sucking foot, instead 

 of a cotyledon, root, and foot, as in the ferns. This embryo 

 remains parasitic on the green gametophyte for a time, but ulti- 

 mately gives rise to the adult sporophyte already described. 

 Life history. The life history of Equisetum (Fig. 180) will be 

 found upon inspection to present the same sequence of stages as 

 that of the fern, together with a close resemblance between the 

 two forms as regards the structure of their reproductive organs 

 and cells. These facts, as stated above, establish the close alliance 

 of the equiseta and the ferns in spite of the great dissimilarity 

 in the form and structure of the adult sporophytes. 



LYCOPODIALES, OR CLUB MOSSES 

 SPOROPHYTE 



Habit. In the Lycopodiales the sporophytes are often mis- 

 taken for mosses on account of their small leaves and their 

 habit of growing in clusters or mats on the forest floor of tem- 

 perate and tropical regions. Their structure and life history, 

 however, indicate clearly that they are near relatives of the 

 ferns and equiseta described above. The Lycopodiales are divided 

 into two closely related families, the lycopods and selaginellas, 

 on account of an important difference in the method of produc- 

 ing their asexual spores. The lycopods, commonly known as 

 ground pines (Fig. 181), bear but one kind of spores, like the 

 ferns and equiseta, but the selaginellas (Fig. 182) produce two 

 kinds of spores in different sporangia on the same plant. In 

 other respects the sporophytes of the two families are quite 

 similar, with their horizontal branching stems creeping over the 

 surface of the ground and with the erect spore-producing shoots 

 (strobili) furnished with the small green leaves characteristic of 

 the order. The entire plant body is anchored to the ground by 

 naked branches sent out from the horizontal stem ; these grow 

 downward and take root in the soil much like the runners of a 

 strawberry plant. 



