14 PROF. MARGARET J. BENSON ON 



To conclude, the evidence in support of the reference of Sphserostovna ovale to 

 Heterangium Grievii may be summed up as follows : — 



1. Association. 



2. Comparative morphology, i.e. resemblance to Lagenostoma. 



3. Strong suggestions of continuity in the only three cases in which sections have 

 been obtained in a suitable plane, of ovules judged by independent evidence to have 

 been still attached to the parent plant. 



In conclusion, I wish to bear testimony to the steady and able help I have had 

 from my laboratory attendant, C. H. Wells, who has made all but two of the 

 preparations used in this paper. 



V. EXPLANATION OF PLATES. 



S. = Scott Collection. 

 R.H.C. = Royal Holloway College Collection. 



Lettering of Figure*. 



a. = archegonium. 

 ab. = abscission layer. 



c. = cupule. 

 ca. = canopy. 

 e.s. = embryo sac. 



/. = frill. 



h. = tongue-sbaped cells at the base of sinus. 

 m. = micropyle. 

 m.e. = mucilage epidermis (Prof. Oliver's "blow-off") 



n. = persistent column of nucellar tissue. 



p. = plinth. 

 p.c. = pollen chamber. 

 pet. = petiole. 



s. = sclerotic hypodermal sheath. 



si. = sinus. 

 •y.6 n = vascular bundle of inner integument. 

 v.b. 2 = vascular bundle of cupule. 

 v.b. 3 = vascular bundle of the pedicel of the ovule. 



to. = wall of the pollen chamber. 



Plate I. Figs. 1-6. 



Fig. 1. Radial section of the upper part of a young specimen of Sphserostoma ovale enclosed in a 

 cupule (a). The lagenostome shows an early phase in the development of the pollen chamber (>.e. excava- 

 tion incomplete). The tongue-like cells (h.) are formed, but the mucilage papilla? are not yet developed on 

 the inner surface of the canopy. Those on the outer surface are not yet dehisced (m.e.). The embryo sac 

 (e.s.) shows traces of an archegonium (a.). Supporting the crests are seen horn-like prolongations of the 

 sclerotic sheath (s.). 



S., C.N., 387x70xf. 



Fig. 2. Drawing from a photograph of the whole section of a young ovule, part of which is represented 

 in fig. 1. 



S., C.N,, 387 x about 30 x f. 



Fig. 3. Part of an obliquely transverse section through the micropyle in the plane plotted on fig. 1. 

 It shows the corresponding crests on the inner and outer surfaces. At this level the sclerotic sheath is 

 interrupted between the pairs of crests. 



R.H.C., C.N., 253 x about 70 x ^ ! . 



