CHAPTER VIII 

 SPERMATOPHYTA 



The spermatophytes constitute the highest and largest division of the 

 plant kingdom, numVjering approximately 196,000 species. They com- 

 prise the two classes Gymnospermae and Angiospermae, the former being 

 not only the older and more primitive group, but by far the smaller one 

 today. Spermatophytes are found in all parts of the world and in the 

 most diverse habitats. Although the angiosperms dominate the land 

 vegetation, they include members that have become aquatic, epiphytic, 

 and, through partial or complete loss of chlorophyll, saprophytic or 

 parasitic. 



All spermatophytes are characterized by the production of seeds, a 

 feature that at once distinguishes them from the lower groups. Like the 

 pteridophytes, they are vascular plants with an independent sporophyte; 

 but in spermatophytes the sporophyte attains its greatest complexity, 

 while the gametophyte is obscure and so reduced that it is entirely depend- 

 ent upon the sporophyte for its nutrition. 



Spermatophytes range in size from the minute floating duckweeds, 

 some no larger than the head of a pin, to the giant redwoods of California 

 and certain eucalypts of Australia, both of which may reach a height of 

 100 m. All modern gymnosperms are woody plants, while the angio- 

 sperms include both woody and herbaceous types. The stem undergoes 

 lateral branching, the branches nearly always arising in the leaf axils. 

 Most commonly the branching is monopodial. Elongation of the root 

 and stem is accomplished by a terminal meristem, never by an apical cell. 

 All seed plants are heterosporous. The microsporangia and megaspo- 

 rangia are borne by members that are essentially foliar in nature but, 

 although homologous with the sporophylls of pteridophytes, are nearly 

 always more highly modified. Among spermatophytes it is customary to 

 designate the microsporophyll as a stamen, the megasporophyll as a carpel, 

 and the megasporangium as an ovule. ^ The megasporangium produces a 

 single functional megaspore. Because the megaspore is not shed, the 

 female gametophyte develops inside the megasporangium. This feature 

 makes seed formation possible. 



In practically all gymnosperms the female gametophyte produces 

 archegonia, but in angiosperms archegonia are eliminated. The male 



'■ Really the megasporangium is only part of the ovule, e.g., the nucellus. 



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