146 SECRETORF RESERVOIRS. 



In the primary parenchyma of the roots of many Lysimachias and INIyrsinese 

 also, and in the secondary parenchyma of many Composit?e, sacs are found as sub- 

 stitutes for the intercellular reservoirs which are present in other parts of the same 

 plants ; their mode of occurrence will be more accurately stated in the subsequent 

 section which deals with these structures. 



The development of the short reslniferous sacs, and especially the history 

 of development of their contents, is still uncertain, and requires thorough in- 

 vestigation. 



I have termed the other category hmg sacs because they either permeate the 

 tissues as long tubes, which are simple, i. e. arise from one greatly elongated cell, 

 retaining its original wall, and are arranged singly or in longitudinal series, or they 

 form long series, which follow a similar course, though the single members of these 

 are but little elongated. These two special forms may graduate into one another 

 in a single plant (e. g. in the Convolvulacese) according to the extension of the 

 members to which they belong. 



INIost of the long sacs here grouped together have been only partially investi- 

 gated, or very unequally in their different relations, it is therefore possible that to 

 a certain extent quite heterogeneous structures stand provisionally side by side ; the 

 features common to them all are sufficiently indicated by the present treatment of 

 them. The contents of the sacs in question, at least when fully developed, usually 

 consist of a milky mass of resinous bodies (in the widest sense) and watery solutions 

 or mucilage. Their distribution varies in special cases ; the rows of sacs in species 

 of Allium and the sacs of the Cinchoneae permeate the parenchyma alone. But 

 most of these structures accompany the vascular bundles or lie in the secondary bast, 

 being arranged more or less similarly to the laticiferous tubes of various families. 

 In many plants, e. g. certain Aroideae and INIusacese (comp. Sect. 47), they occupy 

 exactly the position which is held by the laticiferous tubes in other nearly allied forms, 

 these being absent in the above plants. All this points to a near relationship, both 

 morphological and physiological, with the laticiferous tubes, or at least with certain 

 organs ascribed to this category ; many of the sacs in question are hence frequently 

 described as laticiferous tubes. It has at all events been assumed for many of them 

 that they arise, as is the case with articulated laticiferous tubes, by coalescence of 

 longitudinal rows of cells, a view which is generally incorrect. When however the 

 sacs of this category are arranged in a linear series, e. g. in Convolvulacese, Acer, 

 Allium, it appears that such coalescence may occur here and there for a short 

 distance by perforation of transverse walls, or even of thin pits on the lateral walls ; 

 it is however always difficult to distinguish (and I have not been quite certain in any 

 case) whether the perforations observed are spontaneous, or were formed in the 

 process of preparation. 



The organs to be placed in this category are the following : the series of sacs 

 filled with latex in species of Allium, and perhaps also of Aloe ; those to be described 

 below (Sect. 47) in the AroidecB, and Musacece ; the series of sacs described as 

 'laticiferous vessels' in the Convolvidacece : and closely allied to these in structure and 

 arrangement are those of the SapotacecB (Sideroxylon, Bumelia, Isonandra), those 

 which run along the vascular bundles of many CynarccE, and finally those of Sambucus, 

 Cinchona, Ladenbergia, and Acer. It must remain undecided whether the resiniferous 



