242 - Multicellular Plants 



storage tissue cells possess chloroplasts and 

 continue to carry on photosynthesis as a sec- 

 ondary function; and the vascular tissue of 

 bryophytes is of a very primitive type, which 

 does not approach the efficiency of the true 

 vascular tissues (p. 244) of the ferns and seed 

 plants. 



TRANSITIONAL DEVELOPMENTS: 

 ASCENDANCE OF THE SPOROPHYTE 

 GENERATION 



Among the Bryophyta the gametophyte 

 generation displays a limited fitness to cope 

 with the land environment; and little evolu- 

 tionary progress has been made by Bryophyta 

 in recent geological times. Meanwhile the 

 sporophyte generation of the higher plants 

 evolved an efficient system of specialized 

 organs and tissues; and the modern ferns and 

 seed plants are well adapted to land condi- 

 tions. In this evolution, however, the ga- 

 metophyte generation of the higher plants 

 has retrogressed and become relatively in- 

 significant, from a nutritive point of view. 

 Although the gametophyte (prothallium) of 

 the fern is an independent plant, its nutritive 

 processes are not any more complex than 

 those of the liverwort; and the gametophvtes 

 of the seed plants are microscopic bodies, 

 which are nourished entirely by the tissues 

 of the sturdy land-adapted sporophytes (p. 

 219). In the following sections, therefore, the 

 nutrition of the gametophyte generations will 

 not be considered; and only the nutrition of 

 the sporophytes of the higher plants will be 

 discussed. 



NUTRITIVE ORGANS AND TISSUES OF 

 THE VASCULAR PLANTS 



Collectively the higher land plants, which 

 possess well-defined conducting (vascular) 

 tissties (see below), constitute the phylum 

 Tracheophyta (Chap. 31). These vascular 

 plants, except for some virtually extinct 

 groups (p. 613), are fairly similar as to their 



discussion, however, deals mainly with the 

 Angiospermae, which are the best adapted to 

 land conditions and the most widely distrib- 

 uted of all tracheophytes. 



Tissues of the Vascular Plants. The fol- 

 lowing tissues, classified according to func- 

 tion, are prseent in the vascular plants: 



1. Men's/em Tissue (also called embryonic 

 parenchyma). Meristem tissue has an tin- 

 limited capacity for multiplication and dif- 

 ferentiation; and all the specialized tissues 

 (listed below) are derived from the meristem 

 of the growing points of the plant. Typically 

 the meristem consists of small thin-walled 

 cells, which possess chloroplasts and which 

 divide more or less continuously, forming 

 more meristem. 



2. Epidermal Tissues. Epidermal tissues pro- 

 vide a suitable covering for the various sur- 

 faces of the plant. Typical epidermal cells fit 

 closely together with a minimum of inter- 



Fig. 13-7. Magnified surface view of a Sedum leaf. 

 Each stoma is flanked by a pair of small sausage- 

 shaped guard cells, which fit in among the large 

 irregular epidermal cells. Photograph retouched to 



nutritive tissues and organs. The following clarify outline of the guard cells. 



