PTERIDOPHYTES— FILICALES 



311 



furnish good material. Pteris is easy to orient, because a transverse sec- 

 tion of the leaf will always give longitudinal sections of the sporangia. 

 Aspidium is good for the sorus covered by a peltate indusium. Cyr- 

 tomium falcatum, very common in greenhouses, is even better, and the 

 receptacle is so elongated that there is a fine series of stages in a single 

 sorus (Fig. 101). 



For the youngest stages, 

 take the circinate tips of the 

 leaves. While many sporangia 

 will be cut obliquely, manj^ 

 will show perfect longitudinal 

 sections. 



Marattia, a tropical fern 

 which is likely to be found in 

 botanical gardens, will illus- 

 trate the "synangium" type of 

 sporangium. Angio-pteris, an- 

 other tropical fern, more likely 

 to be found in greenhouses than 

 Marattia, has a sporangium 

 which furnishes an easy transi- 

 tion to that of the Cycadales. 



For the reduction of chro- 

 mosomes, the sections should 

 not be thicker than 5 fx. Os- 

 munda is particularly good for 

 this purpose because the num- 

 ber of chromosomes is com- 

 paratively small. The young 

 sporangia of Osmunda cinnamo- 

 mea and 0. daytoniaiia show 

 the mother-cell stage in the autumn, but the division into spores does 

 not occur until the following spring, in the vicinity of Chicago, the 

 mitotic figures being found during the latter part of April (Fig. 102). 

 0. regalis does not reach the mother-cell stage in the autumn. Mate- 

 rial for mitosis should be collected during the first two weeks in May. 



For the development of a typical sporangium of the eusporangiate 

 type, nothing is better than Botrychium. Buds of B. virginianum tak- 

 en in September or October show sporangia with well-marked sporoge- 



Fig. 100. — Angiopleris evccta: photomicrograph 

 showing a detail of the stele shown in Figure 99. 

 Stained in safranin. Eastman Commercial Ortho 

 film, Wratten E filter (orange) ; Bausch and Lomb 

 8-mm. objective, N.A. 0.50; exposure, IJ seconds. 

 Negative by Dr. P. J. Sedgwick. X60. 



