352 PROCEEDINGS OF THE 



programme might be arranged to occupy some part of the time 

 or space of these meetings, but it was felt that it would be a pity 

 to interfere with their informal character, which affords opportun- 

 ity for helpful intercourse among the members. The excursions 

 have been maintained under Mr. Wilson's able guidance, and he is 

 to be congratulated on the series of records achieved. Dr. Rendle 

 impressed upon the younger members the advantages of field 

 work under the guidance of old hands. With regard to micro- 

 scopic work, he emphasised the point that the production of clear 

 and instructive preparations and photomicrographs should be 

 only means to an end. In many cases where leisure is limited 

 the microscope could be little more than a window through which 

 one gazes into another world to one's great joy and mental relief or 

 entertainment. There are, however, many instances where 

 exceptional skill in microscopical technique has been attained, but 

 in spite of adequate leisure the microscope and camera have re- 

 mained little more than playthings, whereas useful scientific 

 work might be achieved if some definite problem were kept in view. 

 As examples. Dr. Rendle took, first, the study of diatoms, which 

 might consist of the collection of a number of beautiful and 

 interesting organisms, or it might go further and lead to an 

 increased knowledge of form and structure and the description 

 of new forms, or, further, again, to the study of difficult 

 problems in the life processes of the organisms, or by the 

 mathematical study of minute variations Hght could be thrown 

 on some general scientific problems. As a second example, he 

 mentioned the photomicrographs showing the various forms 

 of poUen grains. A careful comparative study of these forms 

 might throw light on the affinities of groups, or be helpful in the 

 problems of hybridisation, there being great uniformity of the 

 grains in some families and great diversity of form in others. 

 The origin of this diversity is a question of special interest, and 

 in this connection Dr. Rendle proposed to examine briefly the 

 development of the pollen grain. Generally speaking, pollen 

 grains are derived from mother-cells by division of the contents 

 into four. The mother-cells arise from sporogenous cells 

 developed from a special layer in the young anthers (archesporial 

 cells). The archesporial cells also give rise to a layer of " tapetal " 

 cells, which are rich in food material, and act as a nurse layer 

 during the development of the pollen. There are two common 



