D.
(D) seed coat.It is of two types :
A. Natural Vegetative propagation
1. Vegetative propagation by stem. e.g. grasses, turmeric, onion, colocasia, potato, gladiolus and crocus.
2. Vegetative propagation by roots. e.g., Tuberous roots of sweet potato, asparagus, tapioca, dahlia and yams (Dioscorea).
3. Vegetative propagation by leaves e.g. Bryophyllum, Begonia, Lilium.
4. Vegetative propagation from reproductive organs. Flower buds of century plant (Agave sp.) develop into bulbils.
B. Artificial vegetative propagation.
1. Cutting e.g. leaf cutting in Bryophyllum.
2. Layering e.g. Jasmine.
3. Grafting e.g. Rose, Mango.
4. Micro-propagation.
5. Gootee e.g. lemon, orange, guava, litchi
Types of gametes : (a) isogametes of Cladophora (b) heterogametes of Fucus (alga) and (c) human beings
(1) Gametogenesis( by meiosis) -Development of male and female gametes which are haploid in nature .
(2) Fertilization- Fusion of the two gametes (haploid cells) to form zygote (diploid cell).
(3) Embryogenesis- Mitotic divisions and cell differentiation of zygote to form embryo. mitosis helps in increasing the cell number and differentiation helps to form specialized tissues and organs.
(4) Development - Growth of embryo to form new individual.
(1) Plants produced by vegetative propagation are genetically similar and constitute a uniform population called as clone.
(2) Plants that have reduced power of sexual reproduction, long dormant period of seed, poor viability can be multiplied by vegetative methods.
(3) Some fruit trees like banana, pineapple that do not produce viable seeds and dub grass which produces small quantity of seeds can be propagated by vegetative methods.
(4) It is a rapid and easier method of propagation.
(5) Good characters can be preserved by vegetative propagation.
(6) Vegetative Propagation can be used to develop Virus Free plants.
(7) Grafting helps in getting an economically important plant having useful characteristic of two different individuals in short time in a single plant.