5 io BOTANY OF THE LIVING PLANT 



individual spores are small and they are cast out in large numbers to 

 fend for themselves. It is then incumbent on each spore, when it 

 germinates, at once to increase its slender store, otherwise it cannot 

 produce gametes, or nourish the resulting germ. Hence the inde- 

 pendent vegetative existence of the gametophyte, and its immediate 

 formation of photosynthetic tissue when it germinates. 



Further, the difference in biological relation of the two generations 

 to water is very marked. The prothallus, which is semi-aquatic, is the 

 less prominent, and its growth is normally limited in size and duration. 

 The Fern-plant, which is definitely terrestrial in structure and function, 

 is in the ascendent, and its growth is unlimited in size and in duration. 

 A Fern is like a man with one foot in the water and one on land. But 

 the foot that is on land is more firmly set than the other. In the 

 Bryophytes, however, the balance is the other way : it is the gameto- 

 phyte-foot that is more securely placed, and the sporophyte is 

 dependent on it, not temporarily, but up to the time of maturity of 

 its spores. There is no doubt that the Pteridophytes are a real 

 advance on the Bryophytes, as regards success in growth on land. 

 The essential features of superiority of the Pteridophytes over the 

 Bryophytes consist, first, in the establishment of the sporophyte as 

 an independent Plant, rooted in the soil : secondly, in the pro- 

 duction of spores, not matured simultaneously and once for all in 

 a single capsule, but in numerous capsules matured independently, 

 and spread over a long period of time, even over many seasons where 

 the plant is perennial. This feature is universal for all the higher 

 types of the Vegetable Kingdom. Its effect is to increase the possible 

 output of spores : and it tends to make fertilisation a more rare 

 event, instead of a recurrent necessity for the survival of the race. 

 This is an obvious advantage for land-living plants which retain 

 their primitive method of fertilisation, as the Ferns do. In point of 

 fact, it is in the larger Pteridophytes, such as the Tree-Ferns, that 

 the climax of numerical production of homosporous spores has been 

 attained. 



For a more explicit description of the Ferns see Primitive Land 

 Plants, Chapters XVI. to XXIII. 



