PEOVISION FOR POSTERITY 177 



discharged, and tlie egg-cell is fertilized by a ciliated 

 spermatozoid, the operation taking place apart from 

 the sporophyte. In other words, the sexual generation 

 begins to develop in attachment to the asexual plant, 

 but its development is completed apart from it. This 

 peculiar feature of the cryptogamic Selaginella is of 

 paramount interest, for it indicates a tendency, and even 

 a start, towards that which is a marked characteristic 

 of all Phanerogamic, or Flowering, plants. In the 

 latter the megaspore (embryo-sac) remains permanently 

 within the megasporangium (ovule) ; it germinates, and, 

 moreover, the ovum is fertilized while in that position: 

 even at this advanced stage the sexual generation is still 

 dependent upon the asexual sporophyte, and the de- 

 pendence actually continues until the seed, containing 

 the embryo-sporophyte and reserve food, is fully 

 ripened. Thus, in the seeds of Phanerogams we find 

 embryo-plants which have been formed and capitalized 

 with a reserve before being discharged by the parent 

 sporophyte. This is, a magnificent provision for pos- 

 terity fraught with great economy ; less is left to chance 

 than in lower plants, and there is a marked reduction of 

 waste. It is in the Phanerogams, too, that we have the 

 greatest specialization and economy in relation to the 

 development of the microspore (pollen grain). The 

 pollen tube enters the ovule, reaching it with unerring 

 precision, and constitutes a covered way for the passage 

 of the fertilizing male element. There is no waste in 

 the production of male elements; instead of giving a 

 roving commission to a great number of freed spermato- 

 zoids, the majority of which are wasted, the Phanero- 

 gams have learned the better way of the pollen tube, 



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