Il6 CLASSIFICATION OF PLANTS 



broad awl shaped and thickly set. The sporophylls are usually borne 

 in a spike with the sporangia on the upper side of the scale-like leaves. 

 The spores are all of one kind. The gametophyte is bisexual. It is a 

 club-shaped saprophytic organism in some cases, in others it forms a flat 

 green thallus. The spermatozoids are provided with two flagellae. The 

 embyro develops a suspensor as in Selaginella. 



290. Order 2. Selaginellacea also all belong to one genus, Selaginella. 

 Most of the species are tropical but a few delicate moss-like forms are 

 found in our forests. The plant resembles lycopodium somewhat but 

 the arrangement of the leaves is usually dorso-ventral. There are fre- 

 quently two dorsal rows of very small leaves and two ventral rows of larger 

 ones. The sporangia are borne in the axils of leaves near the tip of a 

 branch. There are two kinds of spores found in the same spike. Some 

 sporangia contain four megaspores, others numerous microspores. The 

 microspores develop into a prothallium of one cell and an antheridium 

 of eight cells within which a number of spermatozoids, each with two 

 flagellae, are formed. The megaspore develops a small colorless prothal- 

 lium in which a few archegonia are formed. Only one or two of the arche- 

 gonia are fertilized. The embryo develops an appendage, the suspensor, 

 which consists of a row of cells, by which the embryo is pushed down into 

 the nourishing prothallium. 



291. Order 3. The Isoetacece consist of the single genus, Isoetes. The 

 plants are small, with long needle-shaped leaves arranged in a rosette 

 around a short erect stem. The plants are found submerged in water 

 or in wet soil. The sporangia are borne on the inner surface of the leaves, 

 at the base. The outer leaves bear megasporangia, the inner ones micro- 

 sporangia. The spermatozoids are spiral and have a tuft of cilia like 

 those of the ferns. The embryo has no suspensor. 



292. BRANCH IV. Spermatophytes. The three branches of 

 the vegetable kingdom already described are together called 

 Cryptogams and in distinction to them all the higher forms are 

 called Phanerogams. The latter are in general more highly 

 developed, but the distinguishing character is the seed, like 

 which nothing is found among the Cryptogams. In the Phan- 

 erogams the female gamete is developed within the megaspore 

 wall and the egg cell is fertilized and develops an embryo while 

 the megaspore is still within the sporangium and attached to 

 the parent sporophyte. After the embryo is well formed 



