To FAce Page 136. 



EXPLANATION OF PLATE. 



-Fern-prothallium {pr.) developed from the spore (sp.) to which it is still 

 attached. 



-Fern-prothallium {pr.) quite freed from the spore, and bearing the young 

 asexual plant (pi.) u, an archegonium, the oosphere of which has not 

 developed (longitudinal section). 



-Young asexual plant of Salvtnia {pi.) borne on the prothallium {pr.), 

 which has not become quite freed from the macrospore (sp ) 



-Longitudinal section through a macrospore of Is'utis filled with the 

 prothallium which bears an archegonium [ar.) at the apex. 



-Microspore of Iso'ctes, showing formation of antherozooids {dti.) . pr., 

 prothallium-cell. 



-Microspore (Pollen-grain) of Pinm sylvestyrs : pr, prothallium-cell; an., 

 antheridial cell, which will grow out aa the pollen-tube. 



-Pollen-grain of an Angiosperm ; »., nucleus ; /) . prothallium-cell. 



-Ditto, in germination, showing production of pollen-tube 



-Longitudinal section of ovule of a Gy.tinosperm, showing contents of 

 macrospore (embryo-sac), method of fertilisation and development of 

 embryo; /.integument, iin., nucellus . /)., prothallium (endosperm) 

 contained in the embryo-sac: os.. oospore, showing primary cell 

 divisions as result of fertilisation , t , embryo developed from the 

 other oospore with which it is seen to be still connected ; p., pollen- 

 grain germinating in the micropyls ; p.t., pollen-tube which has 

 fertilised the oospheres. 



-Longitudinal section through the young ovule of an Angiosperm Two 

 cells are distinguished by size and contents from the rest of the 

 nucellus ; t. is the primary tapetal cell, ay the archesporium. 



-Later stage of lo. The archesporium has developed into a row of cells, 

 the lowest of which (w.r) will become the embryo-sac. 



-Still later stage of same, showing the ovule, consisting of nucellus {nii ) and 

 outer {o i ) and inner {i i) integuments, and also the contents of the 

 embryo-sac (ma.) , <?,, oosphere , syii.. synergidx ; ant., antipodal cells. 



—Longitudinal section of nucellus of Rosa livida, showing the sporogenous 

 tissue distinguished by great elongation of the cells, large nuclei, 

 and conspicuous cell-contents Tabular tapetal cells, also distinguished 

 by nuclei and contents, are seen above the sporogenous tissue. 



-Sporogenous tissue of a Cycad surrounded by a layer of tapetal cells (/.), 



-Longitudinal section of ovary of Angiosperm at the time of fertilisation ; ov.. 

 ovary-cavity ; o.:., outer integument of ovule; i.i.i 

 containing the mature embryo-sac in A'hich are seen < 

 svH, synergidae. if«/. antipodal cells ; /■ / , pollen-tube 

 from the grain which germinated on the stigma, d 

 through the ovary-cavity and micropyle to the apex 



-Seed of an Angiosperm containing the embryo (c .) surrounded by endosperm 



(,w.). 



—Longitudinal section of nucellus of Casvarina showing development of 

 sporogenous tissue (dark-celled) After Treub. 



-Longitudinal section of sporogenous tissue at a later stage, showing the 

 large macrospores liita.). A tracheid is indicated at t. After Treub 



-Longitudinal section of ovule after passage of pollen-tube; «'.. ovary-cavity ; 

 o.L, i.i., outer and inner integuments; s. ma., sterile macrospores ; 

 f. ma., fertile macrospore containing sexual apparatus; t/r.chalaza ; 

 p.t., pollen-tube passmg down the tissue of the placenta to the chalaza, 

 where it branches, the main branch passing up the tail of a sterile 

 macrospore (not indicated) and becoming attached to the fertile 

 macrospore. The constriction of the pollen-tube is shown. 



rditto; ;;«., nucellus 

 sn , the oosphere. 

 aking its way 

 wn the style and 

 f the nucellus. 



