70 PART I. THE MORPHOLOGY OF PLANTS. [ 16. 



It may be remarked that in some Fungi and Lichens the spores are ap- 

 parently multicellular. This is, however, not actually the case. The apparently 

 multiceUular spores are really aggregates of unicellular spores. 



The spores produced asexual Ij by the sporophyte of any one 

 plant are commonly of one kind only ; when this is the case the 

 plant is said to be homosporous. But in some of the Pteridophyta, 

 and in all Phanerogams, which are therefore said to be hetero- 

 sporous, there are two kinds of asexually produced spores, which 

 differ in size and in the nature of the organisms to which they 

 respectively give rise, and are distinguished as microspores and 

 mao'ospores. In the Phanerogams, the microspores are commonly 

 termed. pollen- grain*] and the macrospores, embryo-sacs. 



16. General Morphology of the Asexual Reproductive 

 Organs. In the great majority of plants the asexual production 

 of spores takes place in the interior of an organ termed a sporan- 

 gium (gonidangium in the gametophyte) : but in some cases (e.g. 

 most Fungi) they are formed by abstraction (see Cell- formation in 

 Part II.) from branches of the shoot. 



Whilst in some plants the asexual production of spores is not 

 limited to any particular portion of the body, in others it is so 

 limited. When this is the case, the portion of the body which 

 performs this function differs more or less widely in form from 

 the vegetative portions, and it is distinguished as the sporophore. 

 When the body is differentiated into root and shoot, the sporo- 

 phore is always part of the shoot. 



In those plants in which the shoot is differentiated into stem 

 and leaf, the development of spores is commonly confined to the 

 leaves. A leaf bearing one or more sporangia is termed a sporo- 

 phyll. 



(a) The Sporangium (incl. Gonidangium). In unicellular plants 

 (e.g. Yeast, Haematococcus) the cell, that is the whole body of the 

 organism, becomes one sporangium. In this case the development 

 of spores closes the life of the organism, for the protoplasm is 

 used in the formation of the spores, and the cell- wall is ruptured 

 to allow of their escape. 



In simple multicellular plants (e.g. Ulva, Ulothrix) each cell 

 eventually acts as a sporangium, giving rise to spores. With the 

 formation of spores the life of each cell is closed ; so that when all 

 the cells have formed spores the life of the organism is ended. 



In plants of higher organization the formation of spores is 

 limited to certain cells, so that the formation of spores no longer 



