GENEEAL MORPHOLOGY OF THE PLANT 11 



segmentation of its body. In the flowering plants the retrogres- 

 sion of the gametophyte is stDl more marked ; they possess two 

 liinds of spore, and each gives rise to its appropriate gameto- 

 pliyte. In all of them the smaU spores, known as Tnicrospores, 

 produce gametophytes consisting of long tubular outgrowths, 

 which during their development bore their way into the structures 

 among which the large spore and its gametophyte are found. 

 These are known as pollen tubes. The gametophyte arising 

 from the large spore or megaspore consists, in one laree section 

 of tlie flowering plants, the Gymnosperms, of a cellular mass 

 csvhioh is developed inside the spore, and completely fills it. In 

 the other section, the Angiosperms, it is similarly hidden in 

 the interior of the spore, but it consists of only a few cells, 

 some of which are not even furnished with oell-walls. 



Above the Thallophyta the cell produced by the fusion of 

 the gametes gives rise to the new individual while still attached 

 to the gametophyte, so that the sporophyte appears to spring 

 out of the latter. The spores, on the other hand, of whatever 

 kind they may be, are generally set free from the sporophyte, so 

 that the gametophyte appears as an independent structure. A 

 marked exception to this rule occurs in the case of the 

 flowering plants. These produce two kinds of spore : the 

 smaller ones are set free and give rise to the gametophyte 

 or poUen tube which bears the male gametes ; the larger ones 

 remain always attached to the sporophyte, each producing its 

 appropriate gametophyte in its interior, and ultimately leading 

 to the formation of a special structure called the seed. 



The body of the plant, whether gametophyte or sporophyte, 

 may show various degrees of complexity of form. It may be 

 evidently divisible into parts, or members, which may be all 

 alike, or may be dissimilar ; or, agam, it may show no such 

 segmentation. In the latter case the plant body is called a 

 thallus ; in the group of the Thallophyta and in some of the lower 

 Liverworts the prominent form of the plant is of this description. 

 In the great majority of cases the body consists of two dis- 

 similar members, characterised by growth in opposite directions ; 

 these are then called the root and the shoot. Both of these 

 generally exhibit appendages springing from the main body ; 

 but while those of the root are like the member from which they 

 arise, those of the shoot may be of two kinds, some like, others 

 unlike, that on which they are borne. Those which are like it 

 are known as branches ; those unlike it, leaves. We can thus 

 distinguish between thalloid shoots and leafy shoots, according 



