Nov., 1905.] The Classification of Plants, II. 387. 



■% 



16. Archegoniates with heterosporous sporophytes and 

 greatly reduced unisexual gametophytes. 



17. Development of the seed hal)it and siphonogamic 

 fertilization. 



18. Seed plants with open carpels without stigmas and 

 with much reduced parasitic gametophytes. 



19. Development of x^losed carpels with stigmas and begin- 

 ning of the conjugation of polar cells with further reduction of 

 the female -gametophyte. 



20. The highest seed plants, representing the extreme of 

 progressive development. 



Taking the living plants which are delimited by definite 

 transition gaps, readily distinguishable, we can recognize seven 

 great groups. These are represented in the above scheme as 

 follows: First group, No. 4; second group, Nos. 0, 7, 8; third 

 group, Nos. 10, 11, 12; fourth group. No. 14; fifth group. No. 10; 

 sixth group, No. 18; seventh group. No. 20. 



The transition from the first to the second group is very 

 gradual and it may sometimes be difficult in practice to place 

 certain species properly, but the progression from nonsexual to 

 sexual plants is so fundamental and apparently so important for 

 all further advance that this mav be regarded as the most 

 important step taken in the entire plant kingdom. The changes 

 in the life cvcle and in the conditions of heredity are very far 

 reaching. It is also important to have this group defined for 

 purposes of general discussion. 



The seven groups may be called subkingdoms. A subkingdom 

 may then be defined as a group which represents a definite stage 

 of evolution in the plant kingdom and which can be delimited 

 from higher or lower groups bv a distinct break or hiatus or by 

 a definite transition involving a progressive change in the life 

 cycle of the individual. 



It becomes necessary to select names for these subkingdoms. 

 Unfortunately the larger groups have not received any very 

 extensive consideration from systematists. No definite system 

 is here attempted but the names given below have for the most 

 part been used in connection with the groups which they 

 represent. 



I. Protophyta. Protophytes. 

 II. Nematophyta. Nematophytes. 



III. Bryophyta. Bryophytes. 



IV. Pteridophyta, Homosporae. Homosporous Pterido- 



phytes. 

 V. Pteridophyta, Heterosporae. Heterosporous Pterid- 



ophvtes. 

 VI. Gymxospermae. Gymnosperms. 

 VII. Angiospermae. Angiosperms. 



