94 MANUAL OP BOTANY 



CHAPTEK II. 



MORPHOLOGY OF THE REPRODUCTIVE OESANS. 



The life of an individual being but limited in its duration, we 

 find various mechanisms developed to continue the existence of 

 the species ; these form the Reproductive Organs. We have seen 

 that nevi' individuals are produced from existing ones by various 

 naethods, which may be grouped into three classes, known 

 respectively as the vegetative, the asexual, and the sexual. 



Instances have already been given of the origination of 

 special adventitious buds upon various parts of plants which, 

 becoming detached from the parent form, can carry on inde- 

 pendent existence. Such are the young plants arising on the 

 stolons or runners of the Strawberry, or on the leaves of 

 Bryophyllum : all such belong to the first group. We have also 

 found that plants produce from time to time special cells which 

 fall away from the parent and are by themselves capable of 

 giving rise to new plants. When these asexual cells occur upon 

 the sporophyte they are termed spores ; when they arise upon the 

 gametophyte, as they do in many Algse and Fungi, ihey are 

 called gonidia. We have noted, further, that in other oases 

 special cells are produced which unite in pairs to form new 

 cells, from which again the new phase of the plant is developed : 

 these are sexual cells or gametes. The two forms are named 

 sporophytes and gavietopliytes, on account of their bearing 

 spores and gametes respectively. The gametophyte, besides 

 bearing its gametes, may also bear asexual cells or gonidia in- 

 distinguishable in their structure and behaviour from the spores 

 of the sporophyte. The sporophyte, however, never gives rise to 

 gametes. 



On germination the asexual cells, whether spores or gonidia, 

 give rise to gametophytes ; in all forms above the Thallophytes 

 the cell (known as a zygote) resulting from the fusion of the 

 gametes develops into a sporophyte. In some thallophytes the 



