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A TEXTBOOK OF THEORETICAL BOTANY 



which inckide all those with pollen tubes. These are not regular systematic 

 classes, because the division cuts across the Gymnospermae, among which 

 there are some primitive types which still retain antherozoids, although they 

 are pollinated like the higher types. 



CLASSIFICATION 



There are three main sub-phyla included in the Spermatophyta : — 



Pteridospermae (Seed-bearing Ferns) (Extinct). Plants with Fern-like 

 leaves on which were borne microsporangia and megasporangia, the 

 latter producing seeds. The sporophylls are not usually distinguish- 

 able from the foliage leaves and are not aggregated together to form 

 a flower (see Volume III). 



Gymnospermae (Naked-seeded Plants) (Living). Plants, mostly trees, 

 in which the sporophylls have been reduced, so that they no longer 

 resemble the foliage leaves, and have been aggregated into strobili 

 or cones, which constitute flowers. The microsporangia and 

 megasporangia are separated usually into diiTerent strobili. The 

 seeds are not enclosed. 



Angiospermae (True Flowering Plants) (Living). Plants which include 

 trees, shrubs and herbs. The sporophylls are aggregated into flowers 

 which may be hermaphrodite, with both microsporangia and mega- 

 sporangia or unisexual with one type of sporangium only. The 

 megasporangia are enclosed in ovaries, which, after the fertilization 

 of the oosphere, ripen into fruits (Fig. 647) (see Volume II). 



Flowering Plant, 



Embryo 



Fertilized egg 

 (Oospore) 



Microsporangium 



(Pollen Sac) Megaspore 



Microspore 

 (Pollen grain) 



'Embryo sac 



'Generative cell 



Fig. 647. — Life-cycle of the Spermatophyta. 



