Heterospory and Seed Habit in Pteridophytes Botany Article Shared by In this article we will discuss about heterospory and seed habit in pteridophytes. Heterospory in Pteridophytes: Most of the Pteridophytes produce one kind of similar spore. Such Peridophytes are known as homosporous and this phenomenon is known as homospory. However, there are some Pteridophytes which produce two different types of spores differing in size, structure and function.
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Evolution of the seed is one of the most crucial adaptations in Phanerogams for successful survival in terrestrial habitat. Seed is the ripened ovule with integuments formed after fertilization. Reduction to a single functional megaspore per sporangium. Retention and germination of megaspore within the megasporangium.
Development of protective layers and nutritive tissue around megasporangium. Development of an embryo sac within the sporangium. Modification of distal end of megasporangium for pollen capture.
Pollination and Siphonogamy Temporary suspension of growth of embryo i. Rounded red circles indicates different steps In this post we will discuss what all stages Pteridophytes successfully completed in forming a seed?
Step 1: Evolution of heterospory. Land plants up to pteridophytes are homosporous. The next big step in evolution was heterospory or formation of two different types of spores, the smaller ones called microspores and the larger ones known as megaspores.
Of the four, only one is retained ensuring enough space, food and greater chance of developing into a healthy female gametophyte. Step 3: Retention and germination of megaspore within the megasporangium. Hence S. In angiosperms, it is retained. Step 4: Development of protective layers and nutritive tissue around megasporangium.
But In Selaginella, nutritive tissue called tapetum is present. Many spore mother cells disintegrate to form nutritive tissue. Megaspore is protected by its wall also but not by an integument. Step 5, 6, 7, 8: 5 Development of an embryo sac within the sporangium. In pteridophytes, further steps towards seed habit are lacking. There is no embryo sac formation. No siphonogamy, therefore water is essential for fertilization In the figure, Solid red circle indicates : successful, dotted circle: to some extend This summarize the successful steps of Pteridophytes towards seed habit.
Temporary suspension of growth of embryo i. Among Pteridophytes, Selaginella rupestris is the most successful species that completed first four steps towards seed habit. Sharing is Caring Please take 5 seconds to Share. Thank you
Heterospory and Seed Habit in Pteridophytes | Botany
Glossopteridales, Voltziales e. Emporia , 7. Cordaitales see figure below. Hypothesis about different lineages The evolutionary connections between gymnosperm groups are uncertain. Especially the position of the Gnetales is not clear. The different gymnosperm groups are either monophyletic or paraphyletic. Their evolutionary relationships to the angiosperms are unclear.
Easy Biology Class
Heterospory and Seed Habitat in Pteridophytes Short Notes Heterospory and Seed Habitat Origin of Seeds and Seed Habitat in Vascular Plants from Heterospory Heterospory is the production of two or more types of spores Heterospory is a condition of the production of more than one type usually two of spores in a single plant. These two types of spore differ in their formation, structure and most importantly its functions and sexuality. In Pteridophytes , these two spores are called as Microspores and Megaspores. Microspores: Microspores are small sized spores produced in large numbers inside the microsporangium. They are male spores which on germination produce male gametophyte. Megaspores: Megaspores are comparatively large spores produced in limited numbers 1 to 4 inside the megasporangium.
Heterospory: History, Origin and Advantages
Evolution of the seed is one of the most crucial adaptations in Phanerogams for successful survival in terrestrial habitat. Seed is the ripened ovule with integuments formed after fertilization. Reduction to a single functional megaspore per sporangium. Retention and germination of megaspore within the megasporangium. Development of protective layers and nutritive tissue around megasporangium. Development of an embryo sac within the sporangium.
Seed Habit its history ,evolution & Lineages
History of Heterospory 2. Incipience of Heterospory 3. Origin 4. Evidences 5. History of Heterospory: Pteridophytes are the first true land plants. Being the first successful colonisers in land habit pteridophytes show both the homospory and heterospory.