50 MICHIGAN ACADEMY OF SCIENCE. 



THE INTERFOLIAK SCALES OF MOXOCOTYLEDONOUS 



AQUATICS. 



MINXA C. DENTON. 



(Abstract.) 



The squamulfie intrafoliacene are transparent scales which are found 

 in the axils of leaves of certain water plants. They occur in all genera 

 and species of certain large groups; these are the Xaiadacese the Pota- 

 mogetonaceaB, the ScheuchzeriaceiTe, the Alismacese, and the Vallis- 

 neriaceie. 



The squamulie are trichomatic in nature, but thev differ from most 

 trichomes in several respects. One of these is the absolute regularity 

 of their occurrence; each and every leaf of the plant is provided with 

 them. Another point is the constancy in the number of squamul8& 

 borne in each leaf axil, which the species always shows. In Elodea 

 Canadensis, for example, there are two spuamulie to each leaf, never 

 more, never fewer. In many plants, however, the number varies within 

 larger or smaller limits. The squamulie arise in pairs, not simultan- 

 eouslv, but successivelv. Thev are often so numerous as to form a 

 crowded circle which passes entirely around the stem in a line just 

 above the leaf insertion. 



The squamula is ordinarily composed of non-chlorophyll parenchy- 

 matous cells; it has a core or midrib which consists of two or several 

 layers of cells, but its margins and apical portion are only one cell 

 thick. The shape of the scale varies with different plants; perhaps 

 the commonest form is lanceolate ovate, often with a verv much elon- 

 gated tip. 



The size varies greatly in different species. In Elodea Canadensis the 

 length is about .3 mm.; in most Potamogetons, .5 mm.; in Zostera 

 marina, 3 mm.; in Scheuchzeria palustris, more than one centimeter. 



The squamula is only a transitory organ. It arises when the leaf to 

 which it belongs is a mere rudiment; soon outstrips the leaf in rapidity 

 of development, and perishes by the time the leaf has reached its 

 maturity-, or perhaps much sooner. From this fact, it is evident that 

 the squamulos must in some way be connected with the nourishment 

 or protection of the young embryonic tissues. 



A number of the marginal and apical cells of most squamulie are 

 engaged in the formation of some sort of slime or mucilage. This fact 

 Schilling* interprets as supplying the chief function of these organs. 

 But the number of cells thus engaged is very small when compared 

 with the total number of cells in the squamulfp, being only 1:200, 

 or in a ratio many times smaller. 



Lastly, the squamula is an organ not incapable of varying its function 

 to suit the conditions in which it finds itself. Such a variation we 

 find in the chlorophyll squamula? of Naias. which differ widely in cell 

 contents, size of cells, and in the size and shape of the whole structure, 

 from the ordinary ]S^aias squamula. 



* Flora, 1894, Untersuchungen Uber die Schleimbildung der Wasserpflanzen. 



