In large seeds with massive reserve-storing cots., as the most advanced seed- 

 stage, as also in many special types, the cotyledons are not so extracted, but remain 

 permanently under ground within the testa, In such case germination is hypogeal\ 

 the hypocotyl remains short, and the plumule erects directly; cf. Oak, Chestnut, 

 Horse-chestnut, Broad Bean ; also in Monocots. with massive endosperm (Date, Coco- 

 nut, Grass-type), the single cotyledon acting as haustorium. 



Cotyledons and Juvenile-leaves : Two symmetrically-paired cots, are normal 

 for Dicots., as great majority of Angiosperms : a single terminal cot. in most Monocots. 

 The shape of the cot. is determined largely by space-factors, foldings, etc., in the seed- 

 cavity, and is often markedly different from the later-formed leaves (Beech, Sycamore). 

 The first leaves of the seedling may be also different from later formations, usually 

 presenting a simpler type of organization ; i. c. entire instead of lobed or compound ; 

 hence termed * Juvenile-leaves' ; but in specialized forms recapitulatory stages of more 

 elaborate leaves may occur ; cf. trifoliate seedling leaves of Ult x, more marked in the 

 fully pinnate seedling leaves of phyllodinous Acacias. 



L I F E-C YCL E. With the growth of the Seedling a new individual is established, 

 absorptive and photosynthetic like the parent-form of soil-plant. The sequence of 

 reproductive stages may be tabulated in such a scheme as : 



I. The conspicuous land-plant to which the name is given bears reproductive 

 shoots as : ........... Flowers ; 



With reproductive leaves, or / \ 



sporopkylls of two kinds, as : . Stamens (micro) Carpels (mega) ; 



these produce \ | 



sporangia of two kinds, as: . Pollen-Sacs (4, micro) Ovules (i or many, 



and these in turn \ \ mf 8 a ) '> 



spores of two kinds, as: . . Pollen-grains (micro) Embryo-sac (i, mega) 



The spores as uninucleate cells close this stage, and they are so far asexual^ 

 since there is no fusion ; the plant bearing them is asexual^ as a spore-producing 



II. The spores germinate to prothallial stages, as decadent, coenocytic, somatic 

 organizations, as : . . . . Male Prothallus Female Prothallus 



(of 3 nuclei) (of 7 (8) nuclei) 



Certain nuclei are set 



apart as sexual units \ \ 



(gametes) : .... Male nuclei Oosphere. 



These unite by an act of 

 fertilization (syngamy) 

 to : ............ Oospore (Zygote) 



The oospore is a uninucleate spore closing this sexual stage, and it germinates 

 directly to give the .......... Embryo. 



The plants producing the sexual cells are so far sexual, and may be termed 

 ^HH*/0/^y/*-generation. The fact that the embryo is closed down to a dormant stage 

 in the seed, does not affect its nature as the new young plant, aroused in germination 

 to get a hold on the soil. The seed-stage is a biological addition of little significance 

 in the life-cycle of reproductive phases. 



The life-cycle thus presents the alternation of a sporophyte stage with a gameto- 

 phyte stage, though the latter is very decadent, and so vestigial that it is hard to follow. 

 The sporophyte generation has diploid nuclei, up to the mother-cells of the tetrads ; 

 the gametophyte has haploid nuclei. Fertilization doubles the chromosome number ; 

 meiotic reduction occurs in the elaboration of asexual spores. 



Phaseolus, seedling 2-3 weeks old ; note strong erected shoot-axis with rapidly 

 elongating first internode ; juvenile foliage-leaves with stipules ; main tap-root with 

 laterals ; testa ruptured, cotyledons hypogeal at first, coming above ground in later 

 stages and developing chlorophyll ; practically no depletion of starchy reserves at this 

 stage. Short hypocotyl ; buds in axils of cotyledons, growing if first leader is damaged. 

 Section of primary root and epicctyl gives primary arrangement of tissues. 



Helianthus : 2 green oval cotyledons, divergent and photosynthetic, carried up 

 by intercalary extension of hypocotyl, 3-4 in. ; root-system feeble, ' fibrous ' : transv. 

 sect, of cotyledon shows green lamina with palisade, and practically no fat left: 

 reserves rapidly metabolized. 



16 



