120 



ELEMENTARY STUDIES IN BOTANY 



strobilus matures, the hard megasporophylls spread apart 

 and the megasporangia become exposed. 



These structures of Seed-plants were known long before 

 the corresponding structures of the lower groups, and of 

 course they received names. It is necessary now to fit the 



two sets of names to- 

 gether, so as to recog- 

 nize what the old names 

 really stand for. The 

 megasporophylls of 

 Seed-plants were called 

 carpels, long before they 

 were known to represent 

 structures belonging to 

 Pteridophytes. Ap- 

 proaching them from 

 the Pteridophytes, we 

 find that the so-called 

 carpel of Seed-plants is 

 a megasporophyll, and 

 this is an illustration of 

 what was meant when 

 it was stated that a 

 lower group of plants 

 explains a higher one. 



The megasporangia of 

 Seed-plants were called 



ovules (the structures that become seeds), and thus we learn that 

 the ovules of Seed-plants are megasporangia. This is im- 

 portant, because ovule means " a little egg," and the thought 

 was that the ovule is an egg. The previous chapters have 

 made it plain that an egg and a sporangium are about as 

 different as two structures can be; not only that, but that 

 the egg belongs to the gametophyte, and the sporangium to 

 the sporophyte. The word " ovule" is not likely to be dis- 



FIG. 96. Ovulate cone of pine : A , cone partly 

 sectioned, showing the central axis and the 

 overlapping carpels ("scales") bearing ovules 

 (megasporangia) near the base ; B and C, 

 single carpels, showing the pair of ovules 

 borne on the upper side. 



