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Botanical Gazette. 



Vol. VI. 



MARCH, 1881. 



No. H. 



Various Forms of Trit-liomes of Ei'liinocystislobata.— in 



reexamining recently the results of a study uf the anatomy of Echino- 

 cystis lobata, Torr. & Gr. , made some years ago, xny attention was at- 

 tracted to the variety of shapes which its trichomes assume. The di- 

 versity is the more unexpected because the plant is "nearly smooth,"* 

 speaking accurately, and what pubescence there is would usually be 

 overlooked. 



Of course, the roots near their tips are provided with the well 

 known, delicate, one-celled root-hairs, which are so abundant and 

 long that when a plantiet is pulled from the ground it brings with it 

 c^uite a weight of soil. 



Few hairs are found on the stem except at the growing extremi- 

 ties. In these places they are numerous, and of two shapes — filiform 

 and ca|)itate. Individually they are minute and delicate although 

 forming a slight pubescence when taken as a whole. They are so 

 evanescent as to rarely persist after the growing point of the stem has 

 extended a few centimeters beyond them. The filiform hairs (PI. I, 

 M, It) are composed of a single row of terete cells, in which move- 

 ments of the ])roloplasm may often be detected under favorable cir- 

 cumstances. They arise from above a hypodermal tissue of coUen- 

 chyma. The capitate form (PI. I, M, st) springs from a parenchyma- 

 tous hypodermal tissue containing chlorophyll. They are much short- 

 er than the first, and consist of a head of two or four large cells side 

 by side supported on a stem of smiller cells. They are more abund- 

 ant than the filiform ones but less persistent. In general, taking the 

 whole plant into consideration, the filiform ones occur ui)on projecting 

 portions of the surface, the ridges and edges, which are firm and with- 

 out stomata : such are the margins of the leaf, the angles of the stem, 

 and the edges o{ the perianth-cup. There are two exceptions to the 

 rule, for they are also found s|)aringly both on the flat surfaces of the 

 leaf, and on the exterior of the perianth-cup. The capitate form 

 springs from stomatic surfaces, e. g. channels of the stem, upper and 

 under surfaces of the leaf, exteri r of the perianth cup, etc., while 

 within the perianth cup, and on the petals are modified forms (describ- 

 ed below) of the some type. 



Full grown leaves are minutely scabrous upon both surfaces from 

 the presence of short, thick, and rigid trichomes, which are sometimes 

 tipped with a minute mucro (PI. I, B). 



A very copious supply of delicate glandular hairs (PI. I, G) upon 

 all sides of the petals gives to them a soft velvety appearance. 



*Grav's Manual, .Ith cd., p. 186: '^nearly glabrous," Fl. North Anier., Toney & Gray 

 V. 1, )J. .MS 



