78 



BOTANY. 



(c) Examples of the simpler forms of laticiferous tissue may be ob- 

 tained for study from Euphwbiacece, Urticacece, Asclepiadacece, Apocy- 

 nacecB. Forms less simple occur in Aracece, and in the maple ; in the 

 last-mentioned they appear to replace the sieve-vessels. Related to 

 these again are the peculiar milk-vessels of the onion (Fig. 66), which 

 consist of elongated cells separated by thin or perforated septa. 



Fig. 67. Longitudinal 

 section through the sieve 

 tissue of Cucurbita Pepo. 

 q, q, section of transverse 

 sieve - plates ; gi, lateral 

 sieve-plate ; as, thin places 

 in wall ; /, the same seen in 

 section ; ps, protoplasmic 

 contents contracted by the 

 alcohol in which the speci- 

 mens were soaked ; sp, pro- 

 toplasm lifted off from the 

 sieve-plate by contraction ; 

 si, protoplasm still in con- 

 tact with the sieve-plate ; z, 

 parenchyma between sieve 

 tubes. X 550. After 

 Sachs. 



(d) The more complex or reticulated forms of laticiferous tissue 

 occur in CicJwriacece, Campanulacece, Lobeliacece, Convolvulacece, Pa- 

 paveracm. 



(e) By heating thin sections of any of the foregoing plants in a di- 

 lute solution of potash the laticiferous tissues may be readily isolated 

 for study. 



(/) The walls of the laticiferous elements are always rich in water, 

 and are composed of cellulose, as may be shown by the blue coloration 

 which follows treatment with Schultz's Solution. 



