loo THE STRUCTURE OF ECONOMIC PLANTS 



Ic 



_; --ep 



B 



par- 



ep---j 



The lactiferous cells end near the extreme base and apex of the 

 leaf respectively, and there is no evidence of any connection between 



them and the vascular bun- 

 -^ J dies or the assimilating tis- 

 sue, nor do they follow the 

 general course of the former. 

 The contents of the cells is a 

 more or less granular turbid 

 fluid which appears on a cut 

 surface of the leaf bases as 

 a pale milky liquid, but is 

 clearer and more watery in 

 the green leaves . The latex 

 does not contain any food 

 substances, according to 

 Rendle, but seems to con- 

 sist of a compound that is 

 easily hydrolyzed to allyl 

 sulphide. Apparently it is 

 an excretion product, and 

 the function of these cells is 

 excretory or protective. 



Owing to the superficial 

 resemblance between the 

 lactiferous cells and sieve 

 tubes, it has been suggested 

 that they may function in 

 conduction; but they appear 

 to be nothing more than 

 rows of excretory sacs that 

 are sealed up by the depo- 

 sition of callus very early 

 in ontogeny. Rendle has 

 observed that "even before 

 the transverse septa become 

 conspicuously pitted, cal- 

 lus-formation occurs upon 

 them; at first usually as 

 small plugs, afterwards often of a more irregular form and sometimes 

 spreading more or less over the whole plate." (Fig. 91, B, C) 





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H 



G 



Fig. 92.. The development of lactiferous cells in 

 Allium. A, longisection of base of young inner 

 leaf; B, tangential section of an inner succulent 

 leaf prior to elongation ; C, tangential sections of 

 base of an outer leaf showing callus formation on 

 transverse septa and occasionally on side walls of 

 cells; D, longisection of a portion of green blade 

 showing location of lactiferous cells ; E, tangential 

 sections of base of an outer succulent leaf showing 

 the pitting in swollen transverse septa; F, tangen- 

 tial section of unelongated leaf showing cross unions 

 between two rows of lactiferous cells ; G, transverse 

 septum from young leaf of the shoot enclosed in a 

 germinating onion : c p, callus plug ; ep, epidermis ; 

 / c, lactiferous cell ; par, chlorophyll parenchyma. 

 (After Rendle, Ann. Bot.) 



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