i6o 



STERILE AND FERTILE REGIONS 



Goethe's theory : it must be enquired whether this is a justifiable assump- 

 tion. This question has not been too exactly scrutinised by his followers, who 

 translated his "progressive metamorphosis" into terms of an evolutionary 

 progression. The basis for the assumption was primarily the succession 

 of events as seen in the individual life of the higher plants ; but a 

 certain laxity of view was further encouraged by the irregularities of 

 number and position and of time of appearance of the sporangia in the 

 Leptosporangiate Ferns. These plants were accorded an undue prominence 

 in the early study of Pteridophytes, and for long the belief was held that 

 they were the prototypes of all Vascular Plants. But it is now sufficiently 

 clear that the Leptosporangiate Ferns are relatively late derivative forms, 

 and that the types of Ferns of the primary rocks were more precise and 



FIG. 85. 



Botrychiuth Lunaria. Sterile laminae, which occasionally produce sporangia (s/>) on 

 certain pinnae, and have partly or wholly assumed the form of the fertile spike : /in 

 B and C is the fertile spike itself. Natural size. (After Goebel.) 



exact in the arrangement and in the time of origin of their sporangia. 

 Such precision is seen in higher degree in the Calamarians and Spheno- 

 phylls, and it is specially prominent in the Lycopods. All of these are 

 types of quite as early, probably of even earlier, geological history than 

 the Leptosporangiate Ferns. Accordingly it may be held that in the 

 earliest Vascular Plants which we know the arrangement, time of appear- 

 ance, and number of the sporangia showed some degree of definiteness, 

 and were in some cases very precise. It cannot be denied that accessory 

 sporangia may at the present day appear in some cases where none are 

 normally present : conspicuous examples are those described by Lang in 

 apogamous Ferns (compare Fig. "35), while a less bizarre case is that of 

 the sporangia which appear on the usually sterile leaf of Botrychium 

 Lunaria (Fig. 85) : abnormal flowers of Phanerogams also provide 

 numerous examples of sporangia not produced in the usual order or 

 position. The question is whether the existence of such cases at the 



