344 TRANS. ST. LOUIS ACAD. SCIENCE. 



of its American representative, /. opaca^ are known to be varia- 

 ble as regards the pungent toothing of their margins, and it has 

 been observed that the upper branches are apt to bear more entire 

 leaves than the lower, as though in correlation with their smaller 

 need of protection, removed, as they are, from the reach of her- 

 bivorous animals, or protected from them by the lowerpart of the 

 plant. As a parallel case, it may be observed that the upper 

 branches of the Osage orange {Madura aurantiaca) are com- 

 monly spineless, while the lower bear spines ; but this, of course, 

 adduces no real proof as to the cause of the observed variability. 



The flowers of both genera are small and not conspicuous, 

 though the petals may be more or less white. All our species 

 appear to be polygamo-dioecious, from the abortion of stamens or 

 pistils.* The cross-fertilization which this separation of the sexes 

 necessitates, is effected by small insects, chiefly Diptera — though 

 Hymenoptera and even Lepidoptera visit them to a certain ex- 

 tentf — attracted by pollen or the very accessible nectar at the base 

 of the flowers. J 



Dissemination is brought about by birds which feed upon the 

 pulpy fruit, the seeds being enclosed within stony, indigestible 

 nutlets. § The red-fruited species often show yellow-fruited races, 

 but these are scarcely more worthy of varietal name than floral 

 albinos of other groups. Parenthetically, it may be said that this 

 remark applies equally to the white-fruited races of Gaylussacia, 

 Fragaria^ &c. 



The Hollies, like many other woody plants now abundant in 

 our flora, appear to have become well established in the Tertiary 

 age. Nemopanthes is said by Schimper to have had one repre 

 sentative at that time,|l and Hex occurred in numerous species 

 which, as a result of the mild climate of high latitudes, reached 

 into the far north of what are now the two great continents, 



* Cf. Darwin; Different Forms of Flowers, 297-8. 



t SeeDelpino: Ult. Osservazione, ii. (2), 300, and Just's Jahresbericht, 1S75, S9;. It 

 is doubtful if tlit-y are at all aneinophilous, as suggested by Meehan in Proc. Philad. Acad. 

 1877, 128. 



X Bonnier states that the entire abortive ovary in male flowers of /. aquifolium serves 

 ^s a nectary. — Ann. So. nat. 1S79, viii. 140. 



§ See Hutli : Kosmos, ix. 2S2, and Verbreitung der Ptlanzen durch die Excremente der 

 Thiere, 1889, 11. Many scattered observations on this subject occur in journals such .ts 

 Nature and Hardwick's Science Gossip. 



II Traite de Paleontol. Veg.— Just. 1S74, 6S0. 



