THE STUDY OF THE EVOLUTION OE THE i'LOWEE. 255 



occupy in the ovary an equivalent morphological position to those of the pluriovulate 



loculi in Symphoricarptis. 



In Diervilla the portion of the ovary corresponding to the parietal region m. Leycesteria 

 is specially developed, the axial portion (H 1} heing relatively small. Hence the greater 

 number of the ovules are parietally home. The opposite placentae are in close contact, 

 so that the ovary is rendered bilocular (H 3). In Diervilla Lonicera the ovules in each 

 loculus are multiseriate (H 2, H 3, ov 1, 2, 3, 4), hut in other species this arrangement is 

 less definite. Diervilla, in the adpressed placentae and multiseriate ovules, differs from 



all other Caprifoliaceae. 



The Ovule. 



Hooker and Thomson * describe ilie ovule of Viburnum Tinm as consisting in its early 

 stages " of a minute curved nucleus encircled with an annulus which is the only integu- 

 ment." This description applies equally well to the Capri foliacese considered in this 

 paper. The nucellus develops more or less obliquely, and is of comparatively small bull 

 At maturity the ovules tend to occupy a tangential position in the loculus 



m.sp 



that 

 nucellus and the vascular bundle of the raphe rest in a plane at right angles to a 

 radial plane. They are not displaced from this position owing to abortion, but in 

 Symphoricarpus the lowermost ovule of each biseriate row may be radially situated with 

 the raphe abaxial, not adaxial as in the Araliacese. 



Vesque in 1878 and Guignard in 1882 record that in Lonicera the embryo-sac is 

 produced from a linear row of three cells. The writer finds that the single megaspore- 

 mother-cell in the sterile ovules of Symphoricarpus, which are morphologically similar to 

 the fertile ovules, produces not a linear row but a group of megaspores (PL 29. figs. 51- 



Complete embryo-sacs were not observed in the sterile ovules. This suggests 

 that thV sterile ovules in Viburnum have become structurally modified in consequence of 

 the loss of fertility, and that the raphe, the integument, and the nucellus have become 

 degenerate. The megaspores of the normal ovule of F. Lantana are arranged in a Hnear 

 row, as described by Hofmeister in his memoir of 1858 ; but the sporogenous tissue of the 

 imperfect ovules originates from one or more subepidermal cells, of which each may 

 produce a group of four cells (PI. 29. figs. 55-57). Each megaspore, as a result of 

 germination, produces an even number of nuclei, usually four or eight; but it is often 

 difficult to trace them to their respective " megaspores," since the nuclei, from eight to 

 sixteen and even more in number, appear to be situated in a single mass of protoplasm 

 (PL 29. figs. 58-60). The energids resulting from the division of the "megaspores" 

 do not become specially modified as in normal embryo-sacs. At the time when the 

 perfect ovule has reached maturity, the energids are grouped to form hollow proto- 



plasmic sacs which subsequently disintegrate. 



Progressive reduction reaches an extreme in Samhums. The tissue swellings, which 

 correspond in situation to biseriate rows of ovules as shown in Text-fig. 3, G4-G8, are 

 caused by the radial elongation beyond the normal of a small plate of sub-epidermal cells 



* Hooker and Thomson, in " Prajcursores ad E 

 SECOND SEEIES. — BOTANY, VOL. VIII. 



(185 



2 



