544f ME. H. MAESHAXL WAEB ON 



Lupmus venusta. 



Fig. 9. Longitudinal section of young ovule, showing rapid tangential divisions 



above and around the embryo-sac mother cell. 



10. Similar preparation of later stage. Further divisions and general elon- 



gation of the nucellus have occurred. 



11, Later stage of same. The enlarging embryo-sac is absorbing all the 



cells around; the nucleus in the centre appears to be the " embryo- 

 sac nucleus." 



Plate XXII. 



(Enot her a biennis. 



Fig. 1. Longitudinal section of young ovule. Embryo-sac mother cell sur- 

 rounded by radiating rows of cells. 



2. Similar preparation, from in front. 



3. Older ovule in longitudinal section, especially showing the radiate ar- 



rangement of the nucellus-cells ; as they near the periphery, radial 

 walls cut up the cells formed by tangential division. 



4. The divided up embryo-sac mother cell of an older ovule : the middle 



diffluent wall appeared first ; then each half again divided. 



Pyrethrum balsaminatum. 



5. Longitudinal section of young floret: the ovule-rudiment in the ovary 



below. 



■ 



6. Older rudiment in longitudinal section : a subepidermal cell above is 



already distinguished by its large nucleus &c. 



7. More advanced ovule in longitudinal section. The integument arises, 



and the ovule becomes anatropous. Two cells are distinguishable by 

 size and granular contents: their nuclei contain bright spherical 

 bodies. 



8 k 9. Similar preparations of more advanced ovules, showing that about 

 three cells fill up the nucleus and elongate with it for some time. 



10 & 11. Similar preparations of more advanced ovule. The integument 

 closes over, and leaves a space above the nucleus ; one cell enlarges 

 much. Fig. 11 is the nucellus of fig. 10 more magnified. 



Plate XXIII. 



Pyrethrum balsaminatum (continued). 



Fig. I. Two of the nucellus-cells appear to enlarge about equally. 



2. Transverse section at similar stage. Two large cells nearly fill up the 



nucellus. 



3. One large cell now occupies the whole of the nucellus : the occurrence of 



more than one nucleus in the protoplasm suggests its origin by ab- 

 sorption of the walls between other cells (cf. fig. 1). 



4. Similar preparation. One cell appears to be absorbing the rest of the 



nucellus 



