70 



BOTANT. 



This tissue makes up the whole of the substance of many 

 of the lower plants. In the higher plants the essential por- 

 tions of the assimilative (green), vegetative (growing), and 

 reproductive parts are composed of parenchyma. 



Instructive examples of parenchyma may be obtained in the growing 

 ends of shoots (Fig. 53) and in the pith of Dicotyledons, in the ends of 

 young roots— (!. g., of Indian corn— in the green pulp of leaves, in tlie 

 pulp of fleshy fruits, and in the substance of young embryos. 



100.— Collenchyma. The 



cells of this tissue are elon- 

 gated, usually prismatic, and 

 their transverse walls are most 

 frequently horizontal, rarely 

 inclined. With few excep- 

 tions* there are no intercellu- 

 lar spaces. The walls are 

 greatly thickened along their 

 longitudinal angles, while the 

 remaining parts are thin (Fig. 

 21, p. 30). The cells con- 

 tain chlorophyll, and retain 

 the power of fission, f Wet 

 specimens show by transmit- 

 ted light a characteristic blu- 

 ish white lustre (Figs. 54 and 

 55). 



Collenchyma is found be- 

 neath the epidermis of Dico- 

 tyledons (and som^ ferns), 

 usually as a mass of conside- 

 rable thickness, and is doubtless developed from parenchyma 

 for the purpose of giving support and strength to the epi- 

 dermis. 



mi 



■Pig. 54. — Transverse pection of collen- 

 chyma (co\ of the Btem of Ef-hinocyatU 

 iobo^ wet with water, and the angles 

 ■greatly swollen, ep, epidermis, with 

 thickened outer wall, x 700. From a 

 drawing by J. 0. Arthur. 



* In tlie collencliyma of SSpJdum perfoliatum there are many lon- 

 gitudinal intercellular spaces of various sizes ; in Ipomcea purpurea 

 there are minute ones. 



f De Bary states that collenohyma-cells are capable of fission. 

 - ' Vergleichende Anatomie der Vegetationsorgane der Phanerogamen 

 und Fame," p. 136. 



