1889.] BOTANICAL GAZETTE. 1QI 



Histology of the leaf of Taxodium. II. 



STANLEY COULTER. 

 (WITH PLATE XI.) 



//. The MesofhylL— The parenchyma of the mesophyll 

 consists of large, irregular, polyhedral cells, characterized 

 bv exceedingly thin walls and numerous infoldings. 1 nese 

 infoldings are usually filiform, although in some instances 

 they are somewhat thickened ; in others, bind ; in otneis, 

 terminated by a knob. Those cells nearest the epidermis 

 and the fibro-vascular bundle have, as a rule, the more num- 

 erous and prominent infoldings. Scattered throughout this 

 tissue are found the so-called » strengthening cells (sclei- 

 enchymatous), either in groups or singly. They seem to be 

 arranged according to definite plan, as in the foliage leat ot 

 Pinusio and the fruit of the Umbellifene", but may be found 

 in almost any part of the leaf. Sections from different leaves 

 rarely show the same arrangement, and the same holds tiue 

 of sections from different parts of the same leal. 1 hey maj , 

 however, be expected in transverse section with a reasonable 

 degree of certainty in two positions, (i) directly over the fibro- 

 vascular bundle, immediately adjoining the epidermal cells 

 of the outer surface of the leaf, and (2) near the ends ot the 

 leaf in its longer diameter. In the first case, they usual!} oc- 

 cur in groups of from 5-20. either massed or arranged in 11- 

 regula? rows, in which arrangement they otten MenUea 

 series of braces for the purpose ot support (tig. 4). in uxc 

 second case, thev may appear singly, as a row stret cmng 

 from the epidermal cells of the outer to those of the innei 

 surface, or as a row running back from the apical cell, in 01 

 parallel to the line of the greater diameter ot the leat ipg-W- 

 It rarely occurs that in this position these cells are more 

 than three "in number, or that they occur otherwise than in a 

 straight line. It sometimes happens that these ceUswe en- 

 tirely absent from this region (fig. 3)1 but this is not tiequenm 



<k« ~ 



the case. 



Groups composed of from three to five cells, rarely more 

 are also found about midway between the epidermis and tl e 

 ibro-vascular bundle, although these are sometimes wantm. 

 It often happens that one-half of the leat will be well sup- 

 plied with these cells, while the other has only one_oi_t^o. 



10 Coulter and Rose, Botanical Gazette, xi. 258. 

 11 Op. oit, xii. 239. 



