Reproduction of Angiospermi ; Theory of Reproduction. rr 



Analogy of Higher Animals: The hs*c*icai line of approach 

 part for reproductive porpoee* in early ontogeny of animal, with tpcoal deveJopa 

 history as 'gametes ', differentiated in two forms (' sei '-distinction) as ; 

 (i) A smaller (microgamete), 5 M or so long, nniniclisliJ, active, with 

 flagellum acting is a posterior propeller, fprrmaiosoon, or sst* 

 produced in euoi mous numbers, 

 (a) A larger (megagamete), is an immotfle spherical cell, nnrimcieite. 100-300 M 

 or more diam. (or even i inch diam. in yolk of ben's eg| 

 tended with reserve food-storage as proteid and fai). the 



gamete j produced in small 



Not, terms, originally applied to the differentiation of the body of an 



il producing the gametes, as male' and ' female', are transferred to the ornns 

 in which the biter are developed, and in more recent times to the gametes themselves, 

 is i quite secondary application. 



Fertilisation, by fusion of two such gametes, extending to fusion of the nuclei 

 (syngamy, nucleogamy), gives a Zygote, as a new cell-unit with 

 A rejuvenated cell is thus produced capable of initiating growth and 

 a new organism of the same general class. 



Afar : Gametes are cells set apart for this special function, and are 

 units, working in terms of stored food-material, if at all, hence short-lived, and 

 soon dying if not used for fertilization. Exceptional cases, more frequent in low 

 organism, imperfectly delimited for the function, may continue metabolism, p 

 phenomena of so-called 'parthenogenesis' or apogamy (cf. ovum of Frog, 

 oosphere of Fucus, apogamy may be induced artificially). 



Meaning of Sexual Fertilisation : Fusion of cell-units of different individuals 

 dates to most remote phases of living organism (in the sea), few phyla being whoUy 

 without it (Bacteria): apparently advantageous from several distinct standpoints: 

 (i) By blending the experiences of two lines of descent, it improves the outlook of the 

 new individual', (2) affording a new stimulus to development ; (3) repeated mingtmg 

 tends to balance up the average of associated individuals, and so *f^hfoh the iwaW 

 standard; (4) it makes for variation owing to subsequent necessity for unrni'i 

 (5) hence may be regarded as the initiator, hastener, and regulator of the 



Sexual Reproduction in Plantar Higher plants follow a 

 progression, but tend to become much more complex. The union of a 

 male gamete (antheronoid) with a large immobile female gamete, held in spherical form 

 by surface-tension (oosphtr<\ as xoidogamic fertilization, occurs in Brown Se 



as in spawning fishes, in the sea ; but is less obvious in higher Land-plants, being 

 replaced first by Fertilization in situ (archegonium of Fern), then by loss of the 

 flagellated mechanism, and fertilization by a tube (Siphonogamy) in Ang 

 All the sexual processes are henceforward of microscopic dimensions, and are 

 within the tissues of the plant, as a means of protection against desiccation 

 to air. Other problems have to be taken into account. 



Reproduction: Plants, as opposed to higher 



mancntly fixed organism, the necessity for Dispersal at some stage 



factor ; more particularly as the attainment of fertilization in situ eliminates any chance 



of dispersal on the part of the female gamete. 



In Land-plants a stage of special unicellular units, set apart for this purpose as 

 air-borne spores, replaces a preceding condition in the sea of water-borne spores, and 

 still older flagellated zoVds which do not fuse (apogamons) ; such spores being cells 



UM 



with a nucleus, borne in a special organ (sporangium), and liberated into the 

 medium by dehiscence of the sporangia] wall 



Alternation of Generations : To cover all these functions in sequence, a stale 

 of alternation is set up, as one individual is set span to produce the asexual spores 



tophyte genera 

 eneration is de 

 ith the product 

 gives rise to the 



(sporophyte generation); and the next one (the gametophyte generation) bean both 

 male and female organs, or only one set (a* or $). A generation is defined as i phase 

 beginning with a uninudeate cell sore, and endin with the roduction of i similar 



beginning with a uninucleate cell (spore), and ending with the production of 

 state (sexually or asexually produced) ; and such a unit 



phase. 



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