CHAPTEK III 



THE MICBOSPOBANGIUM 



THE microsporangia of Angiosperms are embedded struc- 

 tures, and are derived from the outermost layer of the peri- 

 blem. Thus far, the only recorded 

 exceptions to this origin are Naias 

 ftexilis, and probably Zannichellia 15 

 and Lilaea subulata, 18 whose micro- 

 sporangia are claimed by Campbell 

 to be derived from the plerome (Fig. 

 5). The periblem origin of the spo- 

 rangia seems to account for the fact 

 that the archesporium is superficial 

 in Pteridophytes and hypodermal in 

 Spermatophytes. It also accounts for 

 the indifference of the sporangia to 

 the morphological nature of the or- 

 gan upon which they appear. In 

 general, they occur upon a lateral 

 member that holds the same relation 

 to the axis as do the leaves, and in 

 this sense it may be called a leaf-like 

 member. Such sporangia, therefore, 

 may be called foliar, and the struc- 

 ture that bears them a sporophyll. 

 In certain cases, however, the sporan- 

 gia are derived from the periblem 

 of the axis, and such may be called 

 cauline. In each case the resulting 

 organ is a stamen, whether in the po- 

 sition of a leaf or \>f an axis. The freedom with which micro- 

 sporangia are sometimes produced may be illustrated by the 



27 



B 



FIG. 5. Naias flfxilis. A, young 

 stamen showing " integument " 

 and plerome origin of arche- 

 sporium ; sporogenous cells rep- 

 resented with nuclei: x 200. 

 B, later stage; x TO. After 



CAMPBELL. 15 



