NORTH AND CENTRAL AMERICAN COMMELINACE/E— HOLM. 161 



pages, the writer has endeavored to include as much as possible of the structural peculiarities, but 

 in some cases our material proved to be insullicient, thus we felt obliged to confine ourselves to 

 the external structure alone. The object of our research has been to illustrate some biological 

 features of these plants, as, for instance, their life under ground; the development of a rhizome; 

 the contractile power of the roots, besides their ability to store nutritive matters; furthermore, 

 the mechanical support possessed by stem and leaf, the organization of the leaf, with the differen- 

 tiation of the chlorenchyma; the stomata and the various types of hairs, etc. 



Among the plants which have been studied by the writer are two that actually represent the 

 very rarest members of the family: Weldenia and Tradescantia Warszewicziana, both from 

 Guatemala. The material of these was carefully collected and preserved by Mr. Wm. R. Maxon, 

 who so very kindly gave us the privilege of using it for our present investigation. 



The species which we have examined belong to the genera Commelina, Aneilema, Tmantia, 

 Tradescantia, and Weldenia: 



Commelina nudiflora L. District of Columbia: thickets in Brookland. 

 C. Virginiea 1.. District of Columbia: among rocks on the Potomac shore. 

 C. erecta L. Florida: near Eustis. 



C. hirtella Vaiil. District of Columbia: sandy river shore near Marshall Hall. 

 C. dianihifolia D. ('. Texas. 



Aneilema nudiflorum R. Br. Georgia: near Thomasville, introduced. 



Tinantia <<n<>mi\Ui (Torr.) Clarke Texas: at Kerrville, 1,600-2,000 feet altitude, and Alamo Heights. San Antonio. 

 Tradescantia rosea Vent. Florida: in sandy soil near Lake Dot, Eustis. 

 T. Virginica L. District Columbia: among rocks on the Potomac shore. 

 T. seopulorum Rose. Arizona: Oak Creek. 



T. sp. Colorado: in alkaline soil, plains near Denver, 5,000 feet altitude. 

 T. crassifolia Cav. Mexico: Barranca of < luadelajara, 5,000 feet altitude. 



T. pinelorum Greene. Arizona: Kincon Mountains, 7,500 feet altitude, and Huachuca Mountains. 

 T. Floridana Wats. Florida: Hammocks, Lee County. 

 T. micrantha Torr. Texas: Corpus Christi. 



T. Warszewicziana K. et B. Guatemala: Santa Rosa, dry rocks in the open. 



Weldenia Candida S< hult. pil. Guatemala: Volcan de Agua, in line, hard-packed sand, .on rocky slopes within the 

 crater, about 3,600 meters altitude. 



Commelina nudiflora L. 



The Germination. 



Seedlings of C. com munis and cristata were described by Miubel (1. a), and by Klebs (1. c.) 

 referred to his second type, where the sheath of the cotyledon becomes very much prolonged and 

 forms a threadlike organ with the apex remaining inclosed in the seed; other representatives 

 of this same type are: Asphodelus, Dianella, Aristea, and Tradescantia. 



Our figure 1 on Plate I shows the seedling of CoimueHim n "</'T>'>ra, and we notice at once 

 the long, threadlike portion between the sheath (S) and th. 1 apex inclosed in the seed (C); this 

 filiform poition may develop from the side of the sheath, as figured, or near the apex of same. 

 There is a distinct hypocotyl (H), from the middle of which a whorl, of three secondary roots have 

 developed, while several others proceed from the base of the hypocotyl. The primary root (R) 

 persists for a few months and ramifies but sparingly (/■)• At this stage of growth we notice, also. 

 the first internode (I 1 ) with the first leaf (L 1 ). The internal structure of the various organs of 

 the seedling may be described as follows: 



The secondary roots (fig. 14. PI. Ill) are very hairy, but possess no exoderm; the cortex (C) 

 consists only of three layers, and the endodermis (End.) is very thin walled. The pericambium 

 (P) is continuous and surrounds three rays of hadrome (H) alternating with three groups of 

 leptome, of which the proto-leptome cells are plainly visible (PL); the center of the root is 

 occupied by a wide vessel. 



A still more delicate structure is observable in the lateral roots (tig. 15, PI. Ill), where 

 there are only two layers of cortical parenchyma (C) immediately inside the epidermis; the endo- 

 dermis (End.) is also here thinwalled with the Casparyan spots plainly visible, but the pericam- 



