Harold Henry Welch Pearson. 



Ixv 



well qualified he was by training and ability to see things in their true 

 perspective, one is able to realise to some extent how valuable such a digest 

 of his knowledge and mature experience would have been. 



During an enforced halt in Namaqualand Pearson made observations on 

 the internal temperature of Euphorbia virosa and Aloe dichotoma. He found 

 that Euphorbia, with its large-chambered pith, responds more quickly than 

 the Aloe to changes in the external temperature and attains higher maxima. 

 He also investigated the effects of wounding : in Aloe the lowering of the 

 internal temperature is due to evaporation at the surface of water conducted 

 through the water-laden xylem, while in Euphorbia the lowering is due in 

 part to surface evaporation but also to the expansion of gases imprisoned in 

 the pith. 



The accounts of travels published in the ' Geographical Journal,' the 1 Kew 

 Bulletin,' the ' Gardeners' Chronicle ' and elsewhere are admirably written 

 and contain much that is of general interest. Pearson took a prominent part 

 in founding the Botanical Society of South Africa, and in 1915 under his 

 editorship the Cambridge University Press published the first part of the 

 ' Annals of the Bolus Herbarium,' a periodical devoted primarily to work 

 inspired directly or indirectly by Dr. Bolus. Pearson was deeply interested 

 in the economic aspect of his subject and illustrated not only by precept but 

 by example the value of botanical research in relation to agricultural science. 

 With characteristic energy he undertook to attack the " Problem of the 

 Witchweed" with which the Department of Agriculture was faced. The 

 Witchweed — Striga luf.ea, a scrophulariaceous plant — is a root parasite, 

 known by many local names, e.g., the Booibloem, Isona, Mealie gift, etc., 

 which attacks maize crops and causes considerable damage. It is probably a 

 native of South Africa, and its dispersal has been largely determined by the 

 extension of maize cultivation. Pearson, with the assistance of one of his 

 pupils, studied the details of the haustorial structures and their connection 

 with the host ; he also investigated the germination and distribution of the 

 small seeds and made many experimental trials of different methods of 

 dealing with the pest. Previous attempts to germinate the seeds of Striga 

 had been unsuccessful, and Pearson proved that germination occurs only in 

 the presence of the host-plant. His results have not only a scientific value, 

 but they enabled him to draw up a number of practical instructions for the 

 treatment of crops and for the prevention of the disease. 



It was for many years Pearson's ambition to bring about the institution of 

 a National Botanic Garden : he felt that the Municipal Garden of Cape 

 Town, first established as a Botanic Garden in 1848, was wholly inadequate 

 and unworthy of a country second to none in the richness of its sub-tropical 

 vegetation. Many botanists, especially visitors from Europe, had expressed 

 disappointment with the existing state of affairs and deplored the absence of 

 a State Garden comparable with those in other parts of the Empire. The 

 task of influencing public opinion, overcoming misunderstandings, and of 

 enlisting the active co-operation of those in authority was one requiring 



