Nov., 1905.] 
The Classification of Plants, II. 
387 
16. Archegoniates with heterosporous sporophytes and 
greatly reduced unisexual gametophytes. 
17. Development of the seed habit and siphonogamic 
fertilization. 
18. Seed plants with open carpels without stigmas and 
with much reduced parasitic gametophytes. 
19. Development of closed 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. 6, 7, 8; third 
group. Nos. 10, 11, 12; fourth group, No. 14; fifth group. No. 16; 
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 may be regarded as the most 
important -step taken in the entire plant kingdom. The changes 
in the life cycle 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 by 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 verA’ 
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. Protopiiyta. Protophytes. 
II. Nem.-vtophyta. Nematophytes. 
III. Bryophyta. Bryophytes. 
IV. Pteridophyta, Homosporae. Homosporous Pterido- 
phytes. 
V. Pteridophyta, Heterosporae. Heterosporous Pterid- 
ophytes. 
VI. Gymnospermae. Gymnosperms. 
VII. Angiospermae. Angiosperms, 
