296 TRANS. ST. LOUIS ACAD. SCIENCE. 



sistent pedicels, bearing one or two small bracts. The inflores- 

 cence itself shows three different forms, and, according to these, 

 the numerous species of this genus naturally are distributed in 

 three different sections. 



The first section, Singulijlorce^ to which our A. Virginica 

 belongs, bears 'single flowers in a simple, generally slender spike, 

 never crowded as the spikes of the next section are ; each flower 

 is borne in the axil of a bract on a short pedicel, which is distin- 

 guished by a single lateral bractlet. This bractlet is normally 

 sterile, but in monstrous inflorescences may produce secondary 

 and tertiary flowers, which, however, can always be distinguished 

 from those of the next section by never appearing n pairs.* 



The second section, Geminijiorce (gen. Littcea^ Tagliab., Bo- 

 napartea^ Willd., non Ruiz & Pav.), comprises the species which 

 produce flowers in pairs, crowded into a more or less dense spike. 

 From the axil of each primary bract a short or rarely longer (e.g. 

 A. Utahensis) peduncle originates, bearing two opposite lateral 

 bracts (sometimes pushed somewhat towards the main axis), and 

 in their axils the flowers on two short (rarely, e.g. in A. atte- 

 nuata^ Hort. Cels. Paris, 1869, longer) secondary pedicels with 

 bractlets of the third order directed towards the primary bract. 

 These bractlets occasionally bear a second pair of flowers with 

 lateral bractlets of the fourth order, directed inward, and in the 

 axils of these occasionally i^A. attenuata) rudimentary flower- 

 buds are seen. An internal perigonal lobe of the flowers of the 

 primary pair is directed backwards and outwards, towards the 

 margin of the primary bract, and an external lobe towards the 

 bractlet. In rai'e instances the primary peduncle does not ter- 



* I have a plant of this species growing, brought from the woods in this vicinity, which 

 produces its irregularly crowded flowering spikes every year in the same manner. The 

 lateral bractlet usually bears a second flower on a similarly bracted pedicel ; this second 

 bractlet stands either on the dorsal (towards the principal bract) or on the ventral (towards 

 the main axis) side of the little inflorescence; a third flower, if present, is not coeval nor 

 opposed to the second one, but later and higher up, and usually on the upper or inner side 

 of the second flower; if the antholytic development, which then is often combined with fas- 

 ciation, proceeds, parts of the primary flower may become more or less detached and again 

 bear incomplete axillary flowers. — It may here be remarked that the flower of the Singuli- 

 florse is so placed in regard to bract and axis, that an external lobe of the perigon and one 

 carpel are turned towards the bract, and an internal lobe and the commissure of the other 

 two carpels towards the axis. That abnormal stock, however, produces sometimes towards 

 the tip of the spike flowers without a pedicel and without a lateral bractlet; in these one 

 external lobe and one carpel are turned towards the axis. 



