MR. T. Н. CORRY ON ASCLEPIAS CORNUTI. 193 
In the former class there is a correlation of the five nectaries being formed by the 
cuculli and lying opposite the five anthers, of the exserted condition of the entire staminal 
column bearing the anthers which surround the style-table, and of the reflexed or spreading 
condition of the calycine and corolline lobes ; in the latter class the five nectaries alternate 
with the five anthers. 
Repeated allusion has already been made to the fact that pollination is only possible 
by means of insect-agency, or in an artificial manner. Yet, inasmuch as several observers, 
among whom may be cited Ehrenberg *, Adolphe Brongniart T, Schauer, and, more 
recently, Mr. Edward Pott (loc. cit.), have regarded the production of pollen-tubes by the 
pollinium while still unremoved from its cell, and the entrance of these tubes through 
the medium of the truly stigmatic surface into the styles and thence to the ovules, as either 
a possibility or a matter of actual occurrence, the facts at our disposal regarding such 
self-fertilization with the pollinium iz situ deserve a brief consideration. 
Brongniart believed that the lower $ of the pollinium still remains seated in the anther- 
cells while rupture occurs in the middle 1, and he actually figured it sot. He was, 
naturally enough, unable to understand how such rupture could take place without 
the action of a liquid of any kind; in order to account for it, however, he supposed that 
the pollen-tubes were produced either by the gradual development of all the parts of the 
flower, or else, more probably, that the corpusculum and its appendages transmit a liquid, 
which is secreted by the corpuscular furrow of the style-table, into the pollinium, and that 
the entry of this liquid determines the swelling of the pollen-grains $. He never suspected 
the intervention of insects, although Brown had previously expressed his belief in the need 
for its occurrence. Mr. Pott, who is perhaps, in modern times, the strongest, and, indeed 
I may say, the only adherent of this view that self-fertilization is possible under the cir- 
cumstances before enumerated, expresses himself thus concerning it :—-“ There is по 
imperative physical obstacle to self-fertilization | with the parts in situ], the inner membrane 
of the anther being cut away apparently for the purpose of allowing or promoting self- 
fertilization ;" and, further, “ Self-fertilization is absolutely certain, failing insect-friends 
(on which he admits fertilization does largely depend] or violence extracting the pollinia 
before the pollen-tubes are produced." This observer, however, tells us, notwithstanding, 
that in the two species of Asclepias which came under his notice, viz. 4. curassavica, L., 
and A. incarnata, L., “ попе of the pollen-masses while i» situ produced tubes, although 
several of the pollinia in situ had strongly marked granulation, and tendency to rupture 
appeared in those cells adjoining the convex edge." Delpino, who vigorously contests the 
truth of this view, affirms the same thing, and evidently got a similar result; for he tells 
us that “оп no single occasion did he see the pollinia produce pollen-tubes while in situ” ||. 
+ Ehrenberg, ‘ Linnea,’ iv. p. 94, 1829; also “Ueber das Pollen der Asclepiadeen," Trans. Royal Acad. of 
Sciences of Berlin, Nov. 1831, and separately, Berlin, 1831. 
t “ Quelques observations sur la manière dont s’opére la fécondation dans les Asclépiadées," Ann. des Sci. Nat. vol. 
xxiv. 1831, pp. 263-279, pls. xiii. & xiv. A & B. 
t Loc. cit. pl. xiv. fig. 5. 
$ Compare Payer's view of the action of the corpuscular appendages, ‘ Organogénie, vol. i. p. 569, quoted at 
