Vol. VI., No. 39.] BULLETIN OF THE TORREY BoranicaL Cus. [New York, Mch., 1878. 
§ 220. Plants of Western lowa’—We owe an apology to the 
Rev. Robert Burgess, of Ames, Iowa, for delay in publishing a note 
on deficiencies in Arthur’s Catalogue of Iowa plants. The note is 
now rather out of date, but we subjoin a list of the plants sent us, as 
well as we could make out from the specimens, which were not 
always perfect enough for a satisfactory determination. We have 
appended a query mark to those about which we were doubtful: 1. 
Cynthia Virginiana, Don.—z. Coreopsis lanceolata, L. ?—3. Par- 
nassia_ Caroliniana, Mchx.— 4. Linaria Canadensis, Spreng. — 5. 
Arenaria Michauxii, Gray.—6. Viola pedata, L.—7. Salix tristis, 
Ait.—8. Cyperus inflexus, Muhl.—g. Alopecurus geniculatus, L.— 
10. Synthyris Houghtoniana, Benth.—11. Cypripedium parviflorum, 
Salisb. ?—12. Ammania latifolia, L—13. Polygonum incarnatum, Ell. 
—14 Aster Tradescanti, L., var. fragilis. ? ?—15. Osmunda Claytoni- 
ana, L.—16. Festuca nutans, Willd.—16 zs. Festuca elatior, L.—17. 
Senecio canus, Hook. ?—18. Lespedeza hirta, Ell., var. sparsiflora, 
T. & G.—19. Valeriana edulis, Nutt.—z2o. Arabis levigata, DC.— 
21. Arabis hirsuta, Scop.—z2z2. Trifolium reflexum, L.—23. Ceras- 
tium viscosum, L.—24. Lechea, a strict form which seems peculiar 
to the region about the Upper Mississippi.—25. Salix discolor, Muhl. 
—26. Potamogeton fluitans, Roth. ?—27. Hypericum Canadense, 
L., var. major.—28. Menyanthes trifoliata, L.—29. Hemicarpha 
subsquarrosa, Nees. — 30. Physalis Philadelphica, Lam. ? — 31. 
Physalis pubescens, L.—32. Plantago major, L.—33. Euphorbia 
glyptosperma, Eng.—34. Euphorbia serpyllifolia, Pers. >—35. Cycla- 
chaena xanthiifolia, Fres.—36. Artemisia Canadensis, Mchx.—37. 
Poa annua, L.—38. Cyperus diandrus, Torr., var. castaneus.—39. 
Sporobolus cryptandrus, Gray. 
§ 221. Growth of Exogens.—The accepted theory of growth in 
the stems of Exogens, especially in the regions of frost, is that dur- 
ing the period of foliation great activity goes on in the movement of 
the fluids throughout the plants structure, and that during that season 
of activity a new ¢uée of wood is formed around the stem; that this 
new formation is marked by vascular tissue on the inner surface, and 
by a more dense and compact tissue on the outer surface. 
On cross sections of most Exogenous stems, this tube is dis- 
tinctly marked by the different tissues which make up the new 
formation. This new tube of wood is believed to be the result of 
one season’s growth. In the regions of frost this season is the period 
of foliation. 
Hence each marking is made by a period of great activity and a 
period of repose, constituting in the regions of frost an entire year. 
Why this tube should have on its inner surface a lining of porous 
structure, while the outer layer is composed of tissues whose structure 
is more dense, has not been explained. It has been suggested that, 
during the months of February and March the outer layer of bark is 
reptured in the direction of the axis of growth, and hence offers 
little resistance to the expansion of the cambium which results from 
the large deposits of cell material. Under this slight pressure the 
(-~ Coulrar }, Lu pe 2.60 
