2 PLANT MORPHOLOGY 



covered, it was found to be actually more evident in the so-called crypto- 

 gams than in the phanerogams. 



Often all plants above the level of the Thallophyta are grouped 

 together as the Embryophyta, plants in which the zygote gives rise to 

 an embryo that undergoes its early development within either an archego- 

 nium or an embryo sac. A less suitable name for these plants, but one 

 sometimes used, is Cormophyta, meaning "plants with a stem." Many 

 bryophytes have a stem, but it is not homologous with the stem of 

 pteridophytes and spermatophytes. Sometimes the bryophytes and 

 pteridophytes are combined into a single group, the Archegoniatae, a 

 name that is not distinctive because archegonia are present in nearly all 

 gymnosperms, which form the lower class of spermatophytes. A recent 

 tendency is to place the pteridophytes and spermatophytes together 

 under the name of Tracheophyta, which signifies that they are vascular 

 plants. 



Classification of Thallophyta. Some botanists disapprove of the term 

 Thallophyta on the ground that it includes a heterogeneous assemblage of 

 plants which are not closely related. This objection is more valid v/hen 

 the term is applied to one of the four divisions of the plant kingdom 

 rather than to one of two subkingdoms; for the same objection could be 

 raised against the term Embryophyta. A partial solution of the difficulty 

 is to consider the Thallophyta as a subkingdom and to raise the algae and 

 fungi to the rank of divisions, as follows: 



A. Thallophyta 



I. Phycophyta (Algae) 



II. Mycophyta (Fungi) 



B. Embryophyta (Cormophyta) 



I. Bryophyta 



II. Pteridophyta 



III. Spermatophyta 



The thallophytes comprise a number of subordinate groups. These 

 may either be considered as classes and assigned to the algae or the fungi, 

 or may be distributed among a larger number of divisions. The first 

 arrangement is a convenient one, but some of the groups classified as algae 

 or fungi have little in common with the others. Furthermore, it makes 

 the presence or absence of chlorophyll the basis for establishing the two 

 divisions Phycophyta and Mycophyta, a distinction which cannot be 

 maintained among the flagellates, where both green and colorless forms 

 occur. The flagellates were formerly regarded as constituting a distinct 

 class of thallophytes, but are now broken up into a number of separate 

 groups. 



Some of the groups commonly included among the algae and fungi 

 are so distinctive that their separation seems justified. The.se include the 



