Reproductive Structures of Vascular Plants 167 



Filicales 



The position and construction of the sporogenous area or sorus 

 and the character ol the sporophyll differ in the numerous genera. 

 Aspleiiiuin )iidus-(n>i.s. tlie bird's nest fern, bears sori on the large, 

 leathery, entire vegetative leaves, whereas Onoclea struthiopteris, the 

 ostrich fern, bears the sporangia in the tightly infolded, pod-like 

 pinnules of special fertile fronds. 



The preparation of the diverse subjects is practically identical. 

 Select young sori, and examine a dissected portion of a sorus, using 

 stages up to and including young thin-walled spores. Excise small 

 portions of leaf tissue bearing sori, and kill in medium chrome-acetic 

 or Craf II. Species having soft leaves are more economically 

 dehydrated in alcohol or acetone, but butyl alcohol is advisable for 

 the tougher types. Stain in iron hematoxylin to obtain the best nuclear 

 details and in safranin-fast green for general use. Do not waste time 

 embedding mature sporangia. The contents of the sporangium, the 

 construction of the annulus, and the character of the wall of the 

 mature spore are shown far better in a wet mount of fresh or preserved 

 material. Some of the cultivated ferns have a high ratio of shriveled, 

 undeveloped spores in the mature sporangium; sections of such 

 material are disappointing. 



Gametophytes of native ferns can be found in great abundance by 

 an experienced collector. Such materials are useful for gross study, 

 but the presence of soil particles among the rhizoids makes sectioning 

 difficult and unsatisfactory. Gametophytes can be grown on nutrient 

 agar cultures, or on porous clay flowerpots in a moist chamber. 

 Remove a few gametophytes for examination at intervals, kill 

 desirable specimens in medium chrome-acetic or Craf I, and prepare 

 whole mounts (Chap. 10) or embed very carefully for microtome 

 sections. Iron hematoxylin and safranin-fast green yield beautiful 

 preparations. There is no need to section thalli bearing sporophytes, 

 and permanent whole mounts are not so desirable as wet mounts that 

 can be handled and viewed from all angles. 



Gymnospermae 



Members of the common genera of the Coniferales are well-known 

 trees of great economic importance, and abundant material is easily 

 available. The life history of the pine is probably the most widely 

 used subject, therefore, the present discussion will be centered around 

 reproduction in the pine. The reader should consult Chamberlain 



