PLANT PHTSI0L0G7. 115 



acters. The results of fertilization, however, are of a 

 greater degree of coraplexity in the bryophytes and pterido- 

 phytes than in the Charophycese ; while in the latter the 

 result is a singe spore, in bryophytes it is a cylindrical 

 many-celled axis the upper portion of which develops 

 spores by the division of internal cells, and in the pterido- 

 phytes it is an axis terminating in roots below, and bearing 

 leaves above. There is a noticeable immersion of the arche- 

 gone in the tissues of the parent plant in the pteridophytes, 

 and in the gymnosperms there is a complete submergence. 

 At the same time, in the gymnosperms, with the retention 

 of the macrospore within the sporangium (nucellus), and 

 the development of one or two nucellar integuments, there 

 is a still greater increase in the protective tissue surround- 

 ing the oospore. This is carried a step further in the 

 angiosperms where the leaf (carpel) folds over and encloses 

 the coated nucellus (ovule). The results of fertilization in 

 gymnosperms and angiosperms (effected here by the pollen- 

 tube) are little if any higher than in the pteridophytes, 

 consisting in the development of an embryo plant with its 

 root, stem, and leaves. The protective tissues surrounding 

 the embryo, especially those of the seed-coats, are, however, 

 notable additions, made necessary by the fact that the 

 embryo is still to be separated from the parent plant. 



199. Increased Parental Care. — When we take a com- 

 prehensive view of sexual reproduction, we note that as we 

 pass from the lower plants to the higher, there is step by 

 step an increase in the amount of aid given by the parent 

 plant to the new organism. Additional protective devices 

 appear, and the period of parental care is more and more 

 prolonged in successively higher classes. In illustration of 

 this we may contrast the naked resting-spore of a pond 



