SECTIONAL TRANSACTIONS.— K. 381 



This quite naturally explains the absence of tetraspores and tetrasporic plants. 



Where the reduction-division occurs is not yet settled with absolute certainty. 

 It either occurs immediately after fertilisation — probably, however, not in the carpo- 

 gonium itself — or else there are a number of divisions of the diploid nucleus, followed 

 eventually by several reduction-divisions. At the moment it has not been settled 

 which of these two possibilities really holds good. This must be decided in the future. 

 It is, however, a fact that Asparagopsis arniata must be classed among those Floridea? 

 which the author has designated as haplobiontic. 



In the opinion of the author the Floridese should be divided into two main 

 groups : — 



I. Haplobionticce or haplobiontic types, and 



II. Diplobionticoz or diplobiontic types. 



To the former belongs with certainty the majority of the group Nemalionales ; and it 

 may be that the concept haplobiontic Florideae coincide with the group Nemalionales. 



We must always keep in view the possibility of finding the haplobiontic condition 

 among the remaining Floridean families. If this results from apogamy it is of no 

 systematic value. If, on the other hand, it is primary, depending upon the place 

 of occurrence of the reduction-division, it is of great systematic importance. 



It must be emphasised that the Florides are remarkable among the members of 

 the vegetable kingdom in the fact that the place of occurrence of the reduction- 

 division — in other plants quite fixed — is different in the different main sub-groups. 



It is not impossible that future cytological investigation of the Red Alga? may offer 

 us new types regarding the place of the occurrence of the reduction-division. 



However this may be, one thing is certain : the future taxonomy of the Rhodo- 

 phycese will demand cytological investigations to a very high degree. 



Afternoon. 

 Excursion to Bramham Park. 



Friday, September 2. 

 Joint Discussion with Section M on The Control of Plant Diseases. 



Mrs. N. L. Alcock. — 



(1) A short revieiv of past measures in ike control of Plant Diseases in Great Britain 

 and how far successful. 



The rise of American gooseberry mildew. Prof. Salmon's warning against 

 American gooseberry mildew and wart disease. Prof. Somerville and white pine 

 blister rust. The saving of the situation as regards wart disease by the discovery 

 of the immune varieties. Action that succeeded — methods that have not succeeded. 



(2) The present point of view and present administration of control. The essential 

 factors for success in control are : — 



(a) The convinced and willing co-operation of growers. This implies their share 

 in framing legislation. 



To attain this end clearness in. exposition and ability to see the point of view of 

 the grower and realisation of the business value of all control measures must go hand 

 in hand with scientific efficiency in administration. 



(b) Accurate scientific knowledge on the part of those administering control. 



(c) Moderation in policy when framing rules and regulations for ordinary occasions, 

 and brevity and conciseness in all exposition of such rules. 



(d) Drastic measures for extraordinary occasions. 



(3) Some questions for the future. 

 Plant disease control in Agricidture. 



Margin of profit here small. Methods must be (o) certain, (b) easy, (c) cheap. 

 Examples — Bunt and Formalin. 



Seed-borne Diseases. 



Some 70 common diseases carried on seeds. Research needed on treatment. 



Horticulture. 



